Enzyme kinetics is the study of the chemical reactions that are catalyzed by enzymes. In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the reaction are investigated. Studying an enzyme's kinetics can reveal the catalytic mechanism of this enzyme, its role in metabolism, how its activity is controlled, and how a drug or an agonist might inhibit the enzyme. Creative Enzymes is a renowned service provider, supporting many industrial and academic researchers for kinetic studies.
Enzyme kinetics is the study of the chemical reactions that are catalyzed by enzymes. In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the reaction are investigated. Studying an enzyme's kinetics can reveal the catalytic mechanism of this enzyme, its role in metabolism, how its activity is controlled, and how a drug or an agonist might inhibit the enzyme. Creative Enzymes is a renowned service provider, supporting many industrial and academic researchers for kinetic studies. https://www.creative-enzymes.com/service/Enzyme-Kinetics_393.html
Enzyme kinetics is the study of the chemical reactions that are catalyzed by enzymes. In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the reaction are investigated. Studying an enzyme's kinetics can reveal the catalytic mechanism of this enzyme, its role in metabolism, how its activity is controlled, and how a drug or an agonist might inhibit the enzyme. Creative Enzymes is a renowned service provider, supporting many industrial and academic researchers for kinetic studies. https://www.creative-enzymes.com/service/Enzyme-Kinetics_393.html
This presentation deals with basics of enzyme kinetics and introduction to various plots which aid in understanding the mechanism of inhibition of enzymes.
A diffusion-limited enzyme catalyses a reaction so efficiently that the rate limiting step is that of substrate diffusion into the active site, or product diffusion out. This is also known as kinetic perfection or catalytic perfection. Since the rate of catalysis of such enzymes is set by the diffusion-controlled reaction, it therefore represents an intrinsic, physical constraint on evolution (a maximum peak height in the fitness landscape). Diffusion limited perfect enzymes are very rare. Most enzymes catalyse their reactions to a rate that is 1,000-10,000 times slower than this limit. This is due to both the chemical limitations of difficult reactions, and the evolutionary limitations that such high reaction rates do not confer any extra fitness.
History
Introduction
General Principles
Enzyme Assays
Single Substrate Reactions
Substrate Complex
The Velocity equation can be derived from following method
Lineweaver-Burk Plot
Derivation
Enzyme Kinetics as an Approach to Understanding Mechanism
References
This presentation deals with basics of enzyme kinetics and introduction to various plots which aid in understanding the mechanism of inhibition of enzymes.
A diffusion-limited enzyme catalyses a reaction so efficiently that the rate limiting step is that of substrate diffusion into the active site, or product diffusion out. This is also known as kinetic perfection or catalytic perfection. Since the rate of catalysis of such enzymes is set by the diffusion-controlled reaction, it therefore represents an intrinsic, physical constraint on evolution (a maximum peak height in the fitness landscape). Diffusion limited perfect enzymes are very rare. Most enzymes catalyse their reactions to a rate that is 1,000-10,000 times slower than this limit. This is due to both the chemical limitations of difficult reactions, and the evolutionary limitations that such high reaction rates do not confer any extra fitness.
History
Introduction
General Principles
Enzyme Assays
Single Substrate Reactions
Substrate Complex
The Velocity equation can be derived from following method
Lineweaver-Burk Plot
Derivation
Enzyme Kinetics as an Approach to Understanding Mechanism
References
Introduction, Nomenclature of enzymes, Classification of enzymes on the basis of site of action, on the reaction of catalysis and Classification depends upon substrates on they which act, Specificity of Enzymes, Active Site of An Enzyme: 1. Lock-key model 2. Induce fit model, Factors Affecting Enzymes Reaction, Enzyme 1.Inhibition Competitive inhibition, 2. Non-Competitive inhibition, Isoenzymes, Allosteric Enzymes, Co-Factors, Turnover Number of An Enzyme, Pharmaceutical Importance Of Enzymes,
Increasingly, the global food system is under strain, with an increase in the prevalence of polarised obesity and poverty, and increased dependence on chemical fertilizer and pesticides, poor quality foods, environmental degradation, and the loss of biodiversity. As such, many practices are being revised and regenerated. These practices are informed by biochemistry.
Biochemistry is used to enhance plant growth, yield, and quality as a consequence of optimizing fertilizer components. Crop improvement has also been improved by way of increased tolerance to biotic and abiotic stresses, alongside augmented nutritional value.
With knowledge of the mechanism of action of fertilizers, such as nitrates, the use of fertilizer can be optimized to improve plant growth quality. An example of this is the increasing use of biochemical fertilizers including nitrogen fixes, phosphorus potassium, sulfur solubilizers, and various fungi such as mycorrhiza, and Trichoderma, as well as small molecular iron chelators called siderophores that are produced by microbes.
This is thought to ameliorate the effect of intense use of chemical fertilizers, which cause water contamination, depleted nutrients, and soul deterioration.
Biochemistry plays an important role in nutrition and health and is considered to be a powerful unsustainable tool for the improvement of health, reduction of poverty, and hunger in the world. Through the use of sustainable biochemistry, the commercialization of biochemical techniques is considered to be a powerful way of reducing brook global poverty and hunger and improving nutritional delivery across the world.
Increasingly, the global food system is under strain, with an increase in the prevalence of polarised obesity and poverty, and increased dependence on chemical fertilizer and pesticides, poor quality foods, environmental degradation, and the loss of biodiversity. As such, many practices are being revised and regenerated. These practices are informed by biochemistry.
Biochemistry is used to enhance plant growth, yield, and quality as a consequence of optimizing fertilizer components. Crop improvement has also been improved by way of increased tolerance to biotic and abiotic stresses, alongside augmented nutritional value.
With knowledge of the mechanism of action of fertilizers, such as nitrates, the use of fertilizer can be optimized to improve plant growth quality. An example of this is the increasing use of biochemical fertilizers including nitrogen fixes, phosphorus potassium, sulfur solubilizers, and various fungi such as mycorrhiza, and Trichoderma, as well as small molecular iron chelators called siderophores that are produced by microbes.
This is thought to ameliorate the effect of intense use of chemical fertilizers, which cause water contamination, depleted nutrients, and soul deterioration.
Biochemistry plays an important role in nutrition and health and is considered to be a powerful unsustainable tool for the improvement of health, reduction of poverty, and hunger in the world. Through the use of sustainable biochemistry, the commercialization of biochemical techniques is considered to be a powerful way of reducing brook global poverty and hunger and improving nutritional delivery across the world.
Enzymes are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products.
This presentation is about the kinetics of enzyme action , the Michaelis- Menten Model and kinetics of allosteric enzyme action in a simplified language.
Michaelis-Menten Kinetics in Transient State: Proposal for Reversible Inhibit...IJERA Editor
The enzymatic processes according Michaelis-Menten kinetics have been studied from various approaches to
describe the inhibition state. Proposals for inhibition were compared from a generic process, where kinetic
constants have received unitary values, and the numeric value of the concentration of substrate was ten (10)
times higher than the numerical value of the concentration of enzyme. For each inhibition model proposed,
numerical solutions were obtained from nonlinear system of ordinary differential equations, generating results
presents by graphs showing the variation of the enzyme and enzyme complexes, also the variation of substrate
and product of the reaction. Also, was designed a model with performance, indicating similar behavior to that
seen in the Michaelis-Menten kinetics, where complex of reaction is rapidly formed and throughout the process,
tends to decay to zero. Thus, in this new proposed model, the effect of inhibition starts at zero and, throughout
the process, tends to the nominal value of the initial enzyme concentration. Such responses have proved to be
valid for different values of enzyme concentration and process time, showing robustness. The proposed model
was applied to the hydrolysis of disaccharides, providing a setting with conservation of mass of the model at the
end of the process regarding the responses of the carbohydrate concentration.
Blood lipids refer to a group of fatty substances present in blood, mainly including cholesterol and triglycerides. There are generally two forms of cholesterols circulating in the bloodstream: low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Abnormal lipid level in blood is always associated with a number of diseases, such as high blood pressure, coronary arteries, hypothyroidism, type 2 diabetes, obesity, pancreatitis, et al. https://diagnostic-enzymes.creative-enzymes.com/blood-lipids.html
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A protease is an enzyme that helps proteolysis: protein catabolism by hydrolysis of peptide bonds. The native Bacillus licheniformis protease belongs to the serine endopeptidase subtilisin family, which breaks the peptide bond non-specifically under alkaline conditions. The enzyme is active in aqueous solutions and in some organic solvents such as dry octane. The protease is inactivated by serine active-site inhibitors, such as phenylmethylsulfonyl fluoride (PMSF) and diisopropyl fluorophosphate. https://www.creative-enzymes.com/product/native-bacillus-licheniformis-protease_936.html
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Proteinase K is a broad-spectrum serine protease originally isolated from the fungus Engyodontiumalbum (Tritirachium album). The enzyme was named "proteinase K" for its ability to digest keratin. Structural and molecular biology studies suggest that the enzyme belongs to the subtilisin family characterized by a catalytic triad (Asp39-His9-Ser2) in the active site. Proteinase K has no pronounced cleavage specificity and the preferential cleavage site is the peptide bond adjacent to hydrophobic amino acids. https://www.creative-enzymes.com/product/proteinase-k-from-tritirachium-album-limber-recombinant_3427.html
β-Amylase hydrolyzes the a-(1,4)glucan linkages in polysaccharides of three or more a-(1,4)linked D-glucose units. Natural substrates such as starch and glycogen are broken down intoglucose and maltose. β-amylase, also known as starch β-1,4-galactosidase, is an exo-amylase that cleaves the separated a-1,4 bonds from non-reducing ends when acting on starch and produces maltose. Because amylase changes the configuration of C1 in the hydrolysate maltose molecule from alpha type to beta type during the hydrolysis process, it is named β-amylase. https://www.creative-enzymes.com/product/-amylase-food-grade-_3167.html
A protease is an enzyme that helps proteolysis: protein catabolism by hydrolysis of peptide bonds. The nave Bacillus licheniformis protease belongs to the serine endopeptidase subtilisin family, which breaks the peptide bond non-specifically under alkaline conditions. The enzyme is active in aqueous solutions and in some organic solvents such as dry octane. The protease is inactivated by serine active-site inhibitors, such as phenylmethylsulfonyl fluoride (PMSF) and diisopropylfluorophosphate. https://www.creative-enzymes.com/product/native-bacillus-licheniformis-protease_936.html
Proteinase K is a stable and highly reactive serine protease. Evidence from crystal and molecular structure studies indicates the enzyme belongs to the subtilisin family with an active-site catalytic triad (Asp39-His69-Ser224). It is stable in a broad range of environments:pH, buffer salts, detergents (SDS), and temperature. In the presence of 0.1-0.5% SDS, proteinase K retains activity and will digest a variety of proteins and nucleases in DNA preparations without compromising the integrity of the isolated DNA. https://www.creative-enzymes.com/product/proteinase-k-from-tritirachium-album-limber-recombinant_3427.html
Probiotics are living microorganisms that co-exist with humans. Different from pathogenic microorganisms, probiotics are beneficial, and sometimes essential to health. For example, intake of probiotics can increase the number of beneficial bacteria in the intense, maintain the dynamic balance of intestinal flora, and enhance
gastrointestinal health. https://www.creative-enzymes.com/cate/probiotics_99.html
Tn5 Transposase is a hyperactive form of Tn5 transposase. This enzyme can be used to randomly insert Tn5 transposon into target DNA. Robust Tn5 Transposase recognizes inside end sequences, outside end sequences and mosaic end sequences of Tn5 transposon. https://www.creative-enzymes.com/product/tn5-transposase_8479.html
Blood lipids refer to a group of fatty substances present in the blood, mainly including cholesterol and triglycerides. There are generally two forms of cholesterols circulating in the bloodstream: low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Abnormal lipid level in blood is always associated with a number of diseases, such as high blood pressure, coronary arteries, hypothyroidism, type 2 diabetes, obesity, pancreatitis, et al. https://diagnostic-enzymes.creative-enzymes.com/blood-lipids.html
Explore creative enzymes's enzyme products for triglyceride kitCreative Enzymes
A Triglyceride Kit is used to measure triglyceride concentration in mammalian samples. The triglyceride assay is easy and sensitive. Triglycerides are converted to free fay acids and glycerol. Glycerol is then oxidized to generate a product that reacts with a probe to generate colour and fluorescence. Creative Enzymes provides enzymes that are essential to produce triglyceride kits. https://diagnostic-enzymes.creative-enzymes.com/glycerol-3-phosphate-oxidase-from-pediococcus-sp-item-10.html
Creative Enzymes's Diagnostic Enzymes for POC Biosensor Creative Enzymes
Point-of-care testing (POCT) refers to a group of immediate test approaches that are implemented near or at the site of patient care. Various portable and handheld instruments and test kits, or biosensors, have supplemented the POC. Creative Enzymes serves diagnostic enzyme products to optimize your POC biosensors. https://diagnostic-enzymes.creative-enzymes.com/poct-bio-sensor.html
Explore Enzymes Involved in Blood Lipid Metabolism at Creative EnzymesCreative Enzymes
Blood lipids refer to a group of fay substances present in blood, mainly including cholesterol and triglycerides. There are generally two forms of cholesterols circulating in bloodstream: low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Abnormal lipid level in blood is always associated with a number of diseases, such as high blood pressure, coronary arteries, hypothyroidism, type 2 diabetes, obesity, pancreas, et al. https://diagnostic-enzymes.creative-enzymes.com/blood-lipids.html
Probiotics may exhibit antiallergic effects by degradation or structural modification of enteral antigens, stabilization of aberrant microbiota, improvement of the gut-barrier function, secretion regulation of pro-inflammatory mediators, and development of the immune system. https://probiotic.creative-enzymes.com/multi-strain-probiotics/antiallergic-formula.html
As an enzyme expert, Creative Enzymes is engaged in providing the best products and services for worldwide researchers, especially for enzymes modification. Immobilization is one of the most popular methods that were initially developed for biotechnology processes. Creative Enzymes offers enzyme immobilization services with reliable outcomes, improved performance, and surface analysis. https://www.creative-enzymes.com/service/Enzyme-Modification-By-Immobilization_366.html
Creative Enzymes is a worldwide leading company in diagnostic enzymes manufacturing and supply. We are committed to providing our customers with diverse enzyme products and custom enzyme-related services for medical and research diagnosis. Relying on our professional team and state-of-art technologies, we have gained solid reputation for having top of the line products and services.
Creative Enzymes is a professional and experienced supplier of probiotics. In the past decade, Creative Enzymes mainly provides enzyme-related products and services. With the continuous expansion of business areas and scale, we have set foot in other areas and established a sound probiotic production and supply chain. Based on our high-quality products and services, as well as the unique advantages of large-scale production, our probiotic products are widely favored by industrial customers and scientific research customers.
Creative Enzymes is a world-wide provider of the best enzyme products. We now offer medical enzymes for pharmaceutical and diagnostic uses. In contrast to the industrial uses, enzymes of therapeutic uses are requested in relatively lower amounts but at a very high degree of purity and specificity. We have the capability to assure high-quality enzyme products based on our advanced equipment and professional techniques. In the past few years, the reliability of our products has been approved by thousands of customers and scientists. Specialized in the medical industry, the various kinds of enzyme products of Creative Enzymes will support your research in multiple areas.
As an enzyme expert, Creative Enzymes is engaged in providing the best products and services for worldwide researchers, especially for enzymes modification. Immobilization is one of the most popular methods that were initially developed for biotechnology processes. Creative Enzymes offers enzyme immobilization services with reliable outcomes, improved performance, and surface analysis.
Creative Enzymes is a worldwide leading company in diagnostic enzymes manufacturing and supply. We are committed to providing our customers with diverse enzyme products and custom enzyme-related services for medical and research diagnosis. Relying on our professional team and state-of-art technologies, we have gained solid reputation for having top of the line products and services. https://diagnostic-enzymes.creative-enzymes.com/
Creative Enzymes has long demonstrated expertise and reliability in development and establishment of biocatalysis systems. We provide products, services, and consultation covering every step in the whole process of a biocatalyst development, including the design, modification, expression, purification, production, and validation of specific enzymatic or microbial systems that catalyze the desired reactions. https://www.creative-enzymes.com/service/Biocatalysis-Services_67.html
Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
Preoperative Management of Patients on GLP-1 Receptor Agonists like Ozempic and Semiglutide
ASA GUIDELINE
NYSORA Guideline
2 Case Reports of Gastric Ultrasound
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
ARTIFICIAL INTELLIGENCE IN HEALTHCARE.pdfAnujkumaranit
Artificial intelligence (AI) refers to the simulation of human intelligence processes by machines, especially computer systems. It encompasses tasks such as learning, reasoning, problem-solving, perception, and language understanding. AI technologies are revolutionizing various fields, from healthcare to finance, by enabling machines to perform tasks that typically require human intelligence.
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Ve...kevinkariuki227
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
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Recomendações da OMS sobre cuidados maternos e neonatais para uma experiência pós-natal positiva.
Em consonância com os ODS – Objetivos do Desenvolvimento Sustentável e a Estratégia Global para a Saúde das Mulheres, Crianças e Adolescentes, e aplicando uma abordagem baseada nos direitos humanos, os esforços de cuidados pós-natais devem expandir-se para além da cobertura e da simples sobrevivência, de modo a incluir cuidados de qualidade.
Estas diretrizes visam melhorar a qualidade dos cuidados pós-natais essenciais e de rotina prestados às mulheres e aos recém-nascidos, com o objetivo final de melhorar a saúde e o bem-estar materno e neonatal.
Uma “experiência pós-natal positiva” é um resultado importante para todas as mulheres que dão à luz e para os seus recém-nascidos, estabelecendo as bases para a melhoria da saúde e do bem-estar a curto e longo prazo. Uma experiência pós-natal positiva é definida como aquela em que as mulheres, pessoas que gestam, os recém-nascidos, os casais, os pais, os cuidadores e as famílias recebem informação consistente, garantia e apoio de profissionais de saúde motivados; e onde um sistema de saúde flexível e com recursos reconheça as necessidades das mulheres e dos bebês e respeite o seu contexto cultural.
Estas diretrizes consolidadas apresentam algumas recomendações novas e já bem fundamentadas sobre cuidados pós-natais de rotina para mulheres e neonatos que recebem cuidados no pós-parto em unidades de saúde ou na comunidade, independentemente dos recursos disponíveis.
É fornecido um conjunto abrangente de recomendações para cuidados durante o período puerperal, com ênfase nos cuidados essenciais que todas as mulheres e recém-nascidos devem receber, e com a devida atenção à qualidade dos cuidados; isto é, a entrega e a experiência do cuidado recebido. Estas diretrizes atualizam e ampliam as recomendações da OMS de 2014 sobre cuidados pós-natais da mãe e do recém-nascido e complementam as atuais diretrizes da OMS sobre a gestão de complicações pós-natais.
O estabelecimento da amamentação e o manejo das principais intercorrências é contemplada.
Recomendamos muito.
Vamos discutir essas recomendações no nosso curso de pós-graduação em Aleitamento no Instituto Ciclos.
Esta publicação só está disponível em inglês até o momento.
Prof. Marcus Renato de Carvalho
www.agostodourado.com
Basavarajeeyam is an important text for ayurvedic physician belonging to andhra pradehs. It is a popular compendium in various parts of our country as well as in andhra pradesh. The content of the text was presented in sanskrit and telugu language (Bilingual). One of the most famous book in ayurvedic pharmaceutics and therapeutics. This book contains 25 chapters called as prakaranas. Many rasaoushadis were explained, pioneer of dhatu druti, nadi pareeksha, mutra pareeksha etc. Belongs to the period of 15-16 century. New diseases like upadamsha, phiranga rogas are explained.
Explore natural remedies for syphilis treatment in Singapore. Discover alternative therapies, herbal remedies, and lifestyle changes that may complement conventional treatments. Learn about holistic approaches to managing syphilis symptoms and supporting overall health.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
- Video recording of this lecture in English language: https://youtu.be/lK81BzxMqdo
- Video recording of this lecture in Arabic language: https://youtu.be/Ve4P0COk9OI
- Link to download the book free: https://nephrotube.blogspot.com/p/nephrotube-nephrology-books.html
- Link to NephroTube website: www.NephroTube.com
- Link to NephroTube social media accounts: https://nephrotube.blogspot.com/p/join-nephrotube-on-social-media.html
3. PA R T 01
01General Principles
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4. The reaction catalysed by an enzyme uses exactly the same reactants and produces exactly
the same products as the uncatalysed reaction. Like other catalysts, enzymes do not alter
the position of equilibrium between substrates and products.
However, unlike uncatalysed chemical reactions, enzyme-catalysed reactions display
saturation kinetics.
Enzyme kinetics is the study of the chemical reactions that are catalysed by enzymes. In enzyme kinetics, the reaction rate is measured and the
effects of varying the conditions of the reaction are investigated. Studying an enzyme's kinetics in this way can reveal the catalytic mechanism of this
enzyme, its role in metabolism, how its activity is controlled, and how a drug or an agonist might inhibit the enzyme.
General
Principles
Creative Enzymes
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5. For a given enzyme concentration and for relatively low
substrate concentrations, the reaction rate increases linearly
with substrate concentration; the enzyme molecules are largely
free to catalyse the reaction, and increasing substrate
concentration means an increasing rate at which the enzyme
and substrate molecules encounter one another.
However, at relatively high substrate concentrations, the
reaction rate asymptotically approaches the theoretical
maximum; the enzyme active sites are almost all occupied by
substrates resulting in saturation, and the reaction rate is
determined by the intrinsic turnover rate of the enzyme.
Creative Enzymes
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General
Principles
6. The substrate concentration midway
between these two limiting cases is
denoted by Km. Thus, Km is the
substrate concentration at which the
reaction velocity is half of the maximum
velocity.
The two most important kinetic properties of an enzyme
are how easily the enzyme becomes saturated with a
particular substrate, and the maximum rate it can achieve.
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General
Principles
7. PA R T 02
02Enzyme Assays
Creative Enzymes
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8. Spectrophotometric assays observe
change in the absorbance of light between
products and reactants
Enzyme assays are laboratory procedures that measure the rate of
enzyme reactions. Since enzymes are not consumed by the reactions
they catalyse, enzyme assays usually follow changes in the
concentration of either substrates or products to measure the rate of
reaction. There are many methods of measurement.
Radiometric assays involve the
incorporation or release of radioactivity to
measure the amount of product made
over time.
The most sensitive enzyme assays use
lasers focused through a microscope
to observe changes in single enzyme
molecules as they catalyse their
reactions.
Enzyme
Assays
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9. PA R T 03
03Single-substrate Reactions
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10. Enzymes with single-substrate
mechanisms include isomerases such
as triosephosphateisomerase or
bisphosphoglycerate mutase,
intramolecular lyases such as adenylate
cyclase and the hammerhead ribozyme,
an RNA lyase. However, some enzymes
that only have a single substrate do not
fall into this category of mechanisms.
Single-substrate Reactions
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11. As enzyme-catalysed reactions are saturable, their rate of catalysis
does not show a linear response to increasing substrate. If the initial
rate of the reaction is measured over a range of substrate
concentrations (denoted as [S]), the initial reaction rate (v0) increases
as [S] increases, as shown on the right. However, as [S] gets higher,
the enzyme becomes saturated with substrate and the initial rate
reaches Vmax, the enzyme's maximum rate.
The Michaelis–Menten kinetic model of a single-
substrate reaction is shown on the right.
There is an initial bimolecular reaction between the enzyme E and
substrate S to form the enzyme–substrate complex ES. The rate of
enzymatic reaction increases with the increase of the substrate
concentration up to a certain level called Vmax; at Vmax, increase in
substrate concentration does not cause any increase in reaction rate
as there is no more enzyme (E) available for reacting with substrate
(S). Creative Enzymes
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Michaelis–Menten Kinetics
12. Here, the rate of reaction becomes dependent on the ES complex and the reaction becomes a unimolecular reaction with an order of zero. Though
the enzymatic mechanism for the unimolecular reaction can be quite complex, there is typically one rate-determining enzymatic step
that allows this reaction to be modelled as a single catalytic step with an apparent unimolecular rate constant Kcat.
If the reaction path proceeds over one or several intermediates, Kcat will be a function of several elementary rate constants, whereas in the simplest
case of a single elementary reaction (e.g. no intermediates) it will be identical to the elementary unimolecular rate constant K2.
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Michaelis–Menten Kinetics
The apparent unimolecular rate constant Kcat is
also called turnover number and denotes the
maximum number of enzymatic reactions
catalysed per second.
13. Creative Enzymes
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Michaelis–Menten Kinetics
Michaelis–Menten equation: ν0 = d[P]/dt = Vmax[S]/(Km+[S])
• v0 indicates the reaction rate and the activity of the enzyme;
• [S] represents substrate concentration;
• Vmax indicates maximum reaction rate;
• Km is Michaelis constant, Km= (K-1+K2) / k1.
The value of Michaelis constant is equal to the substrate
concentration when the enzyme reaction rate is half of the maximum
reaction rate. Km represents the affinity of the enzyme to the
substrate. A high Km value indicates a weak affinity between E and
S, and a low km value indicates a strong affinity.
14. As shown on the right, this is a linear
form of the Michaelis–Menten
equation and produces a straight line
with the equation y = mx + c with a
y-intercept equivalent to 1/Vmax
and an x-intercept of the graph
representing −1/Km.
The Lineweaver–Burk plot or double reciprocal plot is a common way of
illustrating kinetic data. This is produced by taking the reciprocal of both
sides of the Michaelis–Menten equation.
Linear Plots of the Michaelis–Menten Equation
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Naturally, no experimental values can
be taken at negative 1/[S]; the lower
limiting value 1/[S] = 0 (the y-intercept)
corresponds to an infinite substrate
concentration, where 1/v=1/Vmax as
shown at the right; thus, the x-intercept
is an extrapolation of the experimental
data taken at positive concentrations.
15. The study of enzyme kinetics is important for two basic reasons.
Firstly, it helps explain how enzymes work, and secondly, it helps
predict how enzymes behave in living organisms. The kinetic
constants defined above, KM and Vmax, are critical to attempts to
understand how enzymes work together to control metabolism.
Making these predictions is not trivial, even for simple systems. For
example, oxaloacetate is formed by malate dehydrogenase within the
mitochondrion. Oxaloacetate can then be consumed by citrate
synthase, phosphoenolpyruvate carboxykinase or aspartate
aminotransferase, feeding into the citric acid cycle, gluconeogenesis
or aspartic acid biosynthesis, respectively. Being able to predict how
much oxaloacetate goes into which pathway requires knowledge of
the concentration of oxaloacetate as well as the concentration and
kinetics of each of these enzymes.
Practical Significance of Kinetic Constants
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16. PA R T 04
04Multi-substrate Reactions
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17. Multi-substrate Reactions
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Multi-substrate reactions follow complex rate equations that describe how the substrates bind and in what sequence. The analysis of these reactions is
much simpler if the concentration of substrate A is kept constant and substrate B varied. Under these conditions, the enzyme behaves just like a single-
substrate enzyme and a plot of v by [S] gives apparent KM and Vmax constants for substrate B. If a set of these measurements is performed at
different fixed concentrations of A, these data can be used to work out what the mechanism of the reaction is. For an enzyme that takes two substrates
A and B and turns them into two products P and Q, there are two types of mechanism: ternary complex and ping–pong.
18. Ternary-complex Mechanisms
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In these enzymes, both substrates bind to the enzyme at the same time to produce an EAB ternary
complex. The order of binding can either be random (in a random mechanism) or substrates have to bind
in a particular sequence (in an ordered mechanism). When a set of v by [S] curves (fixed A, varying B)
from an enzyme with a ternary-complex mechanism are plotted in a Lineweaver–Burk plot, the set of lines
produced will intersect.
Enzymes with ternary-complex mechanisms include glutathione S-transferase, dihydrofolate reductase
and DNA polymerase.
19. Ping–pong Mechanisms
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Enzymes with a ping-pong mechanism can exist in two states, E and a chemically modified form of the enzyme E*; this
modified enzyme is known as an intermediate. In such mechanisms, substrate A binds, changes the enzyme to E* by,
for example, transferring a chemical group to the active site, and is then released. Only after the first substrate is
released can substrate B bind and react with the modified enzyme, regenerating the unmodified E form. When a set of v
by [S] curves (fixed A, varying B) from an enzyme with a ping–pong mechanism are plotted in a Lineweaver–Burk plot, a
set of parallel lines will be produced. This is called a secondary plot.
Enzymes with ping–pong mechanisms include some oxidoreductases such as thioredoxin peroxidase, transferases
such as acylneuraminate cytidylyltransferase and serine proteases such as trypsin and chymotrypsin.
20. Multi-substrate Reactions
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1) Intersecting lines indicate that a ternary complex is formed (increasing [S2] will increase Vmax
and decrease Km).
2) Parallel lines indicate a Ping-Pong mechanism (increase in [S2] increases Vmax (and Km) at
regular intervals)
21. PA R T 05
05Non-Michaelis–Menten Kinetics
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22. This behavior is most common in
multimeric enzymes with several
interacting active sites. Here, the
mechanism of cooperation is similar
to that of hemoglobin, with binding of
substrate to one active site altering
the affinity of the other active sites for
substrate molecules.
Some enzymes produce a sigmoid v by [S] plot, which often indicates
cooperative binding of substrate to the active site. This means that the
binding of one substrate molecule affects the binding of subsequent
substrate molecules.
Non-Michaelis–Menten Kinetics
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Positive cooperativity occurs when
binding of the first substrate molecule
increases the affinity of the other active
sites for substrate. Negative
cooperativity occurs when binding of
the first substrate decreases the affinity
of the enzyme for other substrate
molecules.
23. PA R T 06
06Pre-steady-state Kinetics
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24. This approach was first applied to the hydrolysis
reaction catalysed by chymotrypsin. Often, the
detection of an intermediate is a vital piece of
evidence in investigations of what mechanism an
enzyme follows. For example, in the ping–pong
mechanisms that are shown above, rapid kinetic
measurements can follow the release of product P
and measure the formation of the modified enzyme
intermediate E*. In the case of chymotrypsin, this
intermediate is formed by an attack on the substrate
by the nucleophilic serine in the active site and the
formation of the acyl-enzyme intermediate.
In the first moment after an enzyme is mixed with substrate, no product has been formed and no
intermediates exist. The study of the next few milliseconds of the reaction is called pre-steady-
state kinetics. Pre-steady-state kinetics is therefore concerned with the formation and
consumption of enzyme–substrate intermediates (such as ES or E*) until their steady-state
concentrations are reached.
Pre-steady-state Kinetics
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In the figure to the left, the enzyme produces
E* rapidly in the first few seconds of the
reaction. The rate then slows as steady state is
reached. This rapid burst phase of the reaction
measures a single turnover of the enzyme.
Consequently, the amount of product released
in this burst, shown as the intercept on the y-
axis of the graph, also gives the amount of
functional enzyme which is present in the
assay.
25. PA R T 07
07Enzyme Inhibition
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26. Enzyme Inhibition
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Enzyme inhibition refers to the ability to reduce or lose the activity of the enzyme, but does not cause the denaturation of the enzyme protein. Enzyme
inhibition is mainly caused by changes in the chemical properties of the essential groups of the enzyme. Compounds that cause enzyme inhibition are
called inhibitors. It should be noted that enzyme inhibition is different from enzyme inactivation, and inhibitors are also different from denaturants.
Enzyme inhibition includes reversible inhibition and irreversible inhibition.
27. Reversible Inhibition
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Reversible inhibition refers to the temporary loss of enzyme activity caused by the binding of inhibitors to
enzyme proteins in a non-covalent manner. Reversible inhibitors can be removed by physical methods
such as dialysis and can partially or completely restore enzyme activity. Reversible inhibition includes
competitive inhibition, uncompetitive inhibition, non-competitive inhibition, and mixed inhibition.
Competitive
inhibition
Non-competitive inhibition
28. Competitive inhibition can be overcome by sufficiently high
concentrations of substrate, i.e., by out-competing the inhibitor.
However, the apparent Km will increase as it takes a higher
concentration of the substrate to reach the Km point, or half the
Vmax. In non-competitive inhibition, Vmax will decrease due to
the inability for the reaction to proceed as efficiently, but Km will
remain the same as the actual binding of the substrate, by
definition, will still function properly.
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Reversible Inhibition
30. Irreversible inhibition means that the inhibitor covalently binds to the functional
group of the active center of the enzyme, thus inhibiting the activity of the
enzyme. Irreversible inhibitors cannot be removed by physical methods such as
dialysis and restore enzyme activity.
Irreversible inhibitors often contain reactive functional groups such as nitrogen
mustards, aldehydes, haloalkanes, alkenes, Michael acceptors, phenyl
sulfonates, or fluorophosphonates. These electrophilic groups react with amino
acid side chains to form covalent adducts. Irreversible inhibition is different from
irreversible enzyme inactivation. Irreversible inhibitors are generally specific for
one class of enzyme and do not inactivate all proteins; they do not function by
destroying protein structure but by specifically altering the active site of their
target.
Irreversible Inhibition
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31. PA R T 08
08Chemical Mechanism
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32. • Kinetic measurements taken under various solution conditions
or on slightly modified enzymes or substrates often shed light
on this chemical mechanism, as they reveal the rate-
determining step or intermediates in the reaction.
• Isotopes can also be used to reveal the fate of various parts of
the substrate molecules in the final products.
• The chemical mechanism can also be elucidated by examining
the kinetics and isotope effects under different pH conditions,
by altering the metal ions or other bound cofactors, by site-
directed mutagenesis of conserved amino acid residues, or by
studying the behaviour of the enzyme in the presence of
analogues of the substrate(s).
An important goal of measuring
enzyme kinetics is to determine the
chemical mechanism of an enzyme
reaction, i.e., the sequence of
chemical steps that transform
substrate into product.
Chemical
Mechanism
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33. PA R T 09
09Mechanisms of Catalysis
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34. The favoured model for the enzyme–substrate interaction is the
induced fit model. This model proposes that the initial interaction
between enzyme and substrate is relatively weak, but that these
weak interactions rapidly induce conformational changes in the
enzyme that strengthen binding. Mechanisms of catalysis include
catalysis by bond strain; by proximity and orientation; by active-site
proton donors or acceptors; covalent catalysis and quantum
tunnelling.
Enzyme kinetics cannot prove which modes of catalysis are used by
an enzyme. However, some kinetic data can suggest possibilities to
be examined by other techniques. For example, a ping–pong
mechanism with burst-phase pre-steady-state kinetics would suggest
covalent catalysis might be important in this enzyme's mechanism.
Alternatively, the observation of a strong pH effect on Vmax but not
KM might indicate that a residue in the active site needs to be in a
particular ionisation state for catalysis to occur.
Mechanisms of Catalysis
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