. INTRODUCTION
Insecticides are chemicals specifically designed to kill or control insect populations. They are widely used in agriculture, public health, and other industries to protect crops, livestock, and human health from insect-related damage and diseases. Once applied, insecticides undergo various metabolic processes in insects, which can affect their effectiveness and potential environmental impact.
The metabolism of insecticides in insects involves several key mechanisms:
1. Absorption: Insecticides can enter an insect's body through various routes, such as ingestion, contact with the exoskeleton, or inhalation. The mode of entry depends on the formulation and application method of the insecticide.
2. Phase I metabolism: In this initial phase, insecticides are often transformed by enzymes into more polar compounds through processes such as oxidation, reduction, or hydrolysis. These metabolic reactions aim to make the insecticides more water-soluble and facilitate their elimination from the body.
3. Phase II metabolism: Once insecticides undergo phase I metabolism, they may be further conjugated with endogenous compounds such as sugars, amino acids, or glutathione. Conjugation reactions increase the water solubility of the insecticides even more, making them easier to excrete from the insect's body.
4. Detoxification mechanisms: Insects have developed various enzymatic systems to break down insecticides and render them less toxic. For example, insects possess enzymes like cytochrome P450 monooxygenases, esterases, and glutathione-S-transferases, which are involved in the detoxification of many insecticides. These enzymes can modify the chemical structure of insecticides, making them less harmful to the insect.
5. Excretion: Once metabolized, insecticides and their metabolites are eliminated from the insect's body. This process generally occurs through excretory organs such as Malpighian tubules, which function similarly to the kidneys in vertebrates. Insecticides and their metabolites can be excreted in the faeces, urine, or through other excretory pathways.
Microsomal oxidation refers to a type of metabolic reaction that occurs in the microsomes, which are subcellular organelles found in cells. Microsomes contain various enzymes, including cytochrome P450 enzymes, responsible for catalyzing oxidative reactions in the body.
A. Cytochrome P450 enzymes are a family of enzymes involved in the metabolism of a wide range of endogenous and exogenous compounds, including pesticides, toxins, and foreign substances. These enzymes play a crucial role in the oxidation, reduction, and hydrolysis of various molecules, making them more water-soluble and easier to eliminate from the body.
B. Microsomal oxidation mediated by cytochrome P450 enzymes involves the addition of an oxygen atom to a substrate molecule, resulting in the oxidation of the substrate.
Role of Synergists in Resistance ManagementJayantyadav94
Any chemical which in itself is not toxic to insects as dosages used, but when combined with an insecticide greatly enhances the toxicity of insecticide is known as synergist. Process of activation is synergism. Helps in penetration and stabilization of insecticides, and prevents the detoxification of insecticides
This presentation emphasizes development of resistance in insects against insecticides with different mechanisms and metabolic pathways along with some research findings. it also includes resistance management with different strategies.
Role of Synergists in Resistance ManagementJayantyadav94
Any chemical which in itself is not toxic to insects as dosages used, but when combined with an insecticide greatly enhances the toxicity of insecticide is known as synergist. Process of activation is synergism. Helps in penetration and stabilization of insecticides, and prevents the detoxification of insecticides
This presentation emphasizes development of resistance in insects against insecticides with different mechanisms and metabolic pathways along with some research findings. it also includes resistance management with different strategies.
the repeated use of the same chemical which has the same mode of action that leads to the loss of insect sensitivity and also heritable change would occur in the genome nothing but resistance that means the population not able to control with the normal dose need to develop resistant management strategies
Parasitoids and Predators, their attributes.Bhumika Kapoor
Insect parasitoids have an immature life stage that develops on or within a single insect host, ultimately killing the host, hence the value of parasitoids as natural enemies. Adult parasitoids are free-living and may be predaceous. Parasitoids are often called parasites, but the term parasitoid is more technically correct. Most beneficial insect parasitoids are wasps or flies, although some rove beetles (see Predators) and other insects may have life stages that are parasitoids.
where as the Major characteristics of arthropod predators includes adults and immatures are often generalists rather than specialists, they generally are larger than their prey, they kill or consume many prey males, females, immatures, and adults may be predatory and they attack immature and adult prey.
Biological control (from the ecological viewpoint) is, “the action of parasites, predators, or pathogens in maintaining another organism's population density at a lower average than would occur in their absence.”
the repeated use of the same chemical which has the same mode of action that leads to the loss of insect sensitivity and also heritable change would occur in the genome nothing but resistance that means the population not able to control with the normal dose need to develop resistant management strategies
Parasitoids and Predators, their attributes.Bhumika Kapoor
Insect parasitoids have an immature life stage that develops on or within a single insect host, ultimately killing the host, hence the value of parasitoids as natural enemies. Adult parasitoids are free-living and may be predaceous. Parasitoids are often called parasites, but the term parasitoid is more technically correct. Most beneficial insect parasitoids are wasps or flies, although some rove beetles (see Predators) and other insects may have life stages that are parasitoids.
where as the Major characteristics of arthropod predators includes adults and immatures are often generalists rather than specialists, they generally are larger than their prey, they kill or consume many prey males, females, immatures, and adults may be predatory and they attack immature and adult prey.
Biological control (from the ecological viewpoint) is, “the action of parasites, predators, or pathogens in maintaining another organism's population density at a lower average than would occur in their absence.”
Biological oxidation and Electron Transport Chain is the most important and confusing topic in biochemistry metabolism, but here we tried to put it in the simplest way easy to learn. This presentation was guided by Dr. Arpita Patel and made by Miss Nidhi Argade.
Heterotrophic Metabolism
Bacterial Metabolism heterotrophic metabolism is the biological oxidation of organic substances such as glucose to produce ATP and simpler organic (or inorganic) chemicals that the bacterial cell need for biosynthetic or assimilatory activities.
Respiration
Respiration is a kind of heterotrophic metabolism that utilizes oxygen and produces 380,000 calories from the oxidation of one mole of glucose. (Another 308,000 calories are wasted as heat.)
Heterotrophic Metabolism
Bacterial Metabolism heterotrophic metabolism is the biological oxidation of organic substances such as glucose to produce ATP and simpler organic (or inorganic) chemicals that the bacterial cell need for biosynthetic or assimilatory activities.
Respiration
Respiration is a kind of heterotrophic metabolism that utilises oxygen and produces 380,000 calories from the oxidation of one mole of glucose. (Another 308,000 calories are wasted as heat.)
Krebs Cycle
The Krebs cycle is the oxidative mechanism in respiration that fully decarboxylates pyruvate (through acetyl coenzyme A). 15 moles of ATP (150,000 calories) are produced by the route.
Glyoxylate Cycle
The glyoxylate cycle, seen in some bacteria, is a variant of the Krebs cycle. The oxidation of fatty acids or other lipid molecules produces acetyl coenzyme A.
Electron Transport and Oxidative Phosphorylation
ATP is produced in the last stage of respiration by a series of electron transfer processes within the cytoplasmic membrane that drive the oxidative phosphorylation of ADP to ATP. For this process, bacteria utilise a variety of flavins, cytochrome and non-heme iron components, as well as several cytochrome oxidases.
Digital transformation in plant protection leads to
o Increased efficiency: Reduced manual labour, operational costs, improved resource allocation, and optimised workflows.
o Data driven decision making: Farmers can make more informed choices based on data-driven insights, leading to better pest and disease management strategies.
o Automation and predictive analytics: Automation of tasks like pesticide application has reduced human error and resource waste. Predictive analytics models optimise preventive measures.
o Monitoring: Digital solutions enable real-time monitoring by using cell phones.
o Knowledge sharing and innovation: Rapid sharing of knowledge, best practices, and information among farmers, researchers, and stakeholders is possible.
Also, digital transformation opens up avenues for communication among farmers, scientists, and government bodies, resulting in a multitude of indirect benefits: scientists gain better data access, governments improve their policy-making processes, and farmers attain increased crop productivity.
STOCKHOLM Convention on Persistent Organic Pollutants.pdfPrajwal Gowda M.A
Stockholm Convention (also known as Stockholm Declaration) on Persistent Organic Pollutants is an international environmental treaty, signed on 22 May 2001 in Stockholm, Sweden and effective from 17 May 2004, that aims to eliminate or restrict the production and use of persistent organic pollutants (POPs).
Black Soldier Fly: The Star of Insect Farming
The Black Soldier Fly (BSF), Hermetia illucens (L.), is a wasp-like fly from the Stratiomyidae family of the order Diptera. It is native to the tropical regions of South America and is found globally in tropical and warm temperate regions between latitudes 45°N and 40°S. The insect completes its life cycle in around 25 days, consisting of four developmental stages: egg, larva, pupa, and adult. The larvae undergo six instars, where the final instar develops into a mobile, prepupa.
BSF larvae are commercially mass produced for various purposes, viz., fish and livestock feed, organic waste management, chitin production, bioplastic manufacturing, compost preparation, and many other commercial uses. BSF can also be consumed as human feed in a fried or salted state. BSF prepupae are reported to constitute around 36% to 65% of protein content and 4% to 38% of crude fat content, along with various aminoacids and micronutrients. The prepupal stage of BSF has an average nitrogen, phosphorous, and potassium content of 3.26%, 0.98%, and 1.03%, respectively.
The larval stage of BSF is capable of bioconversion of organic wastes such as animal faeces, kitchen waste, vertebrate remains and decompose them into homogeneous substrate in a shorter time period as compared to vermicompost production. Depending on the size and stage of the larvae, type of the substrate available and environmental conditions, the larvae consume around 25 to 500 mg of organic matter per larva on daily basis (Kim et al. 2021). Larvae can be easily mass produced at farm level with minimal space requirements and its prepupae are used as a perfect substitute for the expensive soybean meal and fish meal diets.
The BSF larval frass and its residues are applied as organic fertiliser, which improves the growth and development of plants (Lopes et al. 2022). By diverting organic waste to BSF larvae, the waste is efficiently converted into biomass, significantly reducing methane and other greenhouse gas emissions. Chitin can be produced from the BSF pupal shells, which has many applications in agriculture, textiles, and the pharmaceutical industry. BSF-derived oil has a high concentration of medium-chain saturated fatty acids (27% to 50% total fatty acids), which makes it potentially an ideal substrate for producing high-quality biodiesel. The lactic acid fermented products of BSF possess a high antimicrobial biomass, which inhibits pathogens like Salmonella enterica and Escherichia coli.
Due to its fast growth, reproduction, and ease with which it can be maintained, the BSF has gained recognition as a highly promising insect for farming and thus earned its reputation as the "Star of Insect Farming". BSF farming can be particularly effective in regions with limited access to traditional protein source, which can improve food and nutritional security. Moreover, India’s climate is well suited for BSF.
Invasive pests & their characteristics, Process of invasion, Methods of introduction, Invasion Rules, List of inavsive pests in India- Origin, distribution, Hosts, Damage symptoms, Natural enemies, Locusts & its lifecycle, Prevention and Management strategies of Invasive Pests
Electrophoresis, Light Microscope, Transmission & Scanning electron microscop...Prajwal Gowda M.A
Steps involved in Electrophoresis, Light Microscope, Scanning and Transmission Electron Microscope.
Differences among them, Advantages and Limitations.
UNDERSTANDING WHAT GREEN WASHING IS!.pdfJulietMogola
Many companies today use green washing to lure the public into thinking they are conserving the environment but in real sense they are doing more harm. There have been such several cases from very big companies here in Kenya and also globally. This ranges from various sectors from manufacturing and goes to consumer products. Educating people on greenwashing will enable people to make better choices based on their analysis and not on what they see on marketing sites.
Artificial Reefs by Kuddle Life Foundation - May 2024punit537210
Situated in Pondicherry, India, Kuddle Life Foundation is a charitable, non-profit and non-governmental organization (NGO) dedicated to improving the living standards of coastal communities and simultaneously placing a strong emphasis on the protection of marine ecosystems.
One of the key areas we work in is Artificial Reefs. This presentation captures our journey so far and our learnings. We hope you get as excited about marine conservation and artificial reefs as we are.
Please visit our website: https://kuddlelife.org
Our Instagram channel:
@kuddlelifefoundation
Our Linkedin Page:
https://www.linkedin.com/company/kuddlelifefoundation/
and write to us if you have any questions:
info@kuddlelife.org
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The carbon cycle is a critical component of Earth's environmental system, governing the movement and transformation of carbon through various reservoirs, including the atmosphere, oceans, soil, and living organisms. This complex cycle involves several key processes such as photosynthesis, respiration, decomposition, and carbon sequestration, each contributing to the regulation of carbon levels on the planet.
Human activities, particularly fossil fuel combustion and deforestation, have significantly altered the natural carbon cycle, leading to increased atmospheric carbon dioxide concentrations and driving climate change. Understanding the intricacies of the carbon cycle is essential for assessing the impacts of these changes and developing effective mitigation strategies.
By studying the carbon cycle, scientists can identify carbon sources and sinks, measure carbon fluxes, and predict future trends. This knowledge is crucial for crafting policies aimed at reducing carbon emissions, enhancing carbon storage, and promoting sustainable practices. The carbon cycle's interplay with climate systems, ecosystems, and human activities underscores its importance in maintaining a stable and healthy planet.
In-depth exploration of the carbon cycle reveals the delicate balance required to sustain life and the urgent need to address anthropogenic influences. Through research, education, and policy, we can work towards restoring equilibrium in the carbon cycle and ensuring a sustainable future for generations to come.
Characterization and the Kinetics of drying at the drying oven and with micro...Open Access Research Paper
The objective of this work is to contribute to valorization de Nephelium lappaceum by the characterization of kinetics of drying of seeds of Nephelium lappaceum. The seeds were dehydrated until a constant mass respectively in a drying oven and a microwawe oven. The temperatures and the powers of drying are respectively: 50, 60 and 70°C and 140, 280 and 420 W. The results show that the curves of drying of seeds of Nephelium lappaceum do not present a phase of constant kinetics. The coefficients of diffusion vary between 2.09.10-8 to 2.98. 10-8m-2/s in the interval of 50°C at 70°C and between 4.83×10-07 at 9.04×10-07 m-8/s for the powers going of 140 W with 420 W the relation between Arrhenius and a value of energy of activation of 16.49 kJ. mol-1 expressed the effect of the temperature on effective diffusivity.
Diabetes is a rapidly and serious health problem in Pakistan. This chronic condition is associated with serious long-term complications, including higher risk of heart disease and stroke. Aggressive treatment of hypertension and hyperlipideamia can result in a substantial reduction in cardiovascular events in patients with diabetes 1. Consequently pharmacist-led diabetes cardiovascular risk (DCVR) clinics have been established in both primary and secondary care sites in NHS Lothian during the past five years. An audit of the pharmaceutical care delivery at the clinics was conducted in order to evaluate practice and to standardize the pharmacists’ documentation of outcomes. Pharmaceutical care issues (PCI) and patient details were collected both prospectively and retrospectively from three DCVR clinics. The PCI`s were categorized according to a triangularised system consisting of multiple categories. These were ‘checks’, ‘changes’ (‘change in drug therapy process’ and ‘change in drug therapy’), ‘drug therapy problems’ and ‘quality assurance descriptors’ (‘timer perspective’ and ‘degree of change’). A verified medication assessment tool (MAT) for patients with chronic cardiovascular disease was applied to the patients from one of the clinics. The tool was used to quantify PCI`s and pharmacist actions that were centered on implementing or enforcing clinical guideline standards. A database was developed to be used as an assessment tool and to standardize the documentation of achievement of outcomes. Feedback on the audit of the pharmaceutical care delivery and the database was received from the DCVR clinic pharmacist at a focus group meeting.
Micro RNA genes and their likely influence in rice (Oryza sativa L.) dynamic ...Open Access Research Paper
Micro RNAs (miRNAs) are small non-coding RNAs molecules having approximately 18-25 nucleotides, they are present in both plants and animals genomes. MiRNAs have diverse spatial expression patterns and regulate various developmental metabolisms, stress responses and other physiological processes. The dynamic gene expression playing major roles in phenotypic differences in organisms are believed to be controlled by miRNAs. Mutations in regions of regulatory factors, such as miRNA genes or transcription factors (TF) necessitated by dynamic environmental factors or pathogen infections, have tremendous effects on structure and expression of genes. The resultant novel gene products presents potential explanations for constant evolving desirable traits that have long been bred using conventional means, biotechnology or genetic engineering. Rice grain quality, yield, disease tolerance, climate-resilience and palatability properties are not exceptional to miRN Asmutations effects. There are new insights courtesy of high-throughput sequencing and improved proteomic techniques that organisms’ complexity and adaptations are highly contributed by miRNAs containing regulatory networks. This article aims to expound on how rice miRNAs could be driving evolution of traits and highlight the latest miRNA research progress. Moreover, the review accentuates miRNAs grey areas to be addressed and gives recommendations for further studies.
WRI’s brand new “Food Service Playbook for Promoting Sustainable Food Choices” gives food service operators the very latest strategies for creating dining environments that empower consumers to choose sustainable, plant-rich dishes. This research builds off our first guide for food service, now with industry experience and insights from nearly 350 academic trials.
1. Insect Toxicology and Residues
WELCOME
Speaker : Prajwal Gowda M.A
Roll No : 12292
Ph.D. : 1st year
Course-incharge :
Dr. Suresh M. Nebapure
(Senior Scientist)
DIVISION OF ENTOMOLOGY
ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE
NEW DELHI - 110 012
METABOLISM AND MICROSOMAL OXIDATION
OF INSECTICIDES
2. When insecticides are applied, they undergo various metabolic processes in insects, resulting in
the formation of new products called metabolites. This process is known as metabolism.
The metabolism of insecticides in insects involves:
1. Absorption: Insecticides can enter an insect's body through various routes.
a) Activation : The metabolic reaction that converts an inactive compound to an active
compound or an active compound to another active compound.
b) Detoxification : The metabolic reaction that converts the compound in to non toxic
compounds.
2. Detoxification mechanisms: Insects have various enzymatic systems (cytochrome P450
monooxygenases, esterases, and glutathione-S-transferases) to break down insecticides and
render them less toxic.
3. Phase I metabolism: In this initial phase, insecticides are often transformed by enzymes into more
polar compounds.
4. Phase II metabolism: Once insecticides undergo phase I metabolism, they may be further
conjugated, making them easier to excrete from the insect's body.
4. Phase I reactions: (Non synthetic)
1. Oxidation : This class includes all those enzymes in which one atom of a
molecule of oxygen is reduced to water while the other is used to oxidize
the substrate. This takes place by mixed function oxidases.
2. Reduction : In these reactions halogen is replaced by hydrogen atom.
3. Hydrolytic processes : These takes place chiefly by esterases. Three
types of esterase are found in insects namely phosphatases,
carboxyesterases and carboxyamidases.
4. Glutathione mediated reaction : In this reactions glutathione is utilized
either in a purely catalytic manner or consumed by the direct binding to
the substrate.
5. Phase 2 reactions are known as "conjugation or synthetic" because the metabolites
are conjugated with glucuronic acid, sulphate, acetyl, methyl, and glycine moieties,
which are large in size and strongly polar in nature.
Phase 2 reactions are of the following types:
• Type I: Insecticide / metabolite + Activated conjugating agent Conjugated product
Type I is very common, and occurs in almost all pesticides which include such
conjugations with methyl, acetyl, glucuronides, glucosides, and sulfates.
• Type II: Activated Insecticide /metabolite + conjugating agent Conjugated product.
Consist of amino acid conjugations.
• Type III: Reactive Insecticide / metabolite + reduced glutathione Conjugated product.
In this type of conjugation, the insecticides or their metabolites possess certain
chemical groups such as halogens, alkenes, NO2, epoxides, aliphatic and aromatic
compounds.
6. i). Glutathione conjugation : In these reactions the harmful electrophilic compounds are
conjugated with GSH (reduced glutathione). This is type III reaction. It is carried out by
glutathione-S-transferase (GST).
ii). Glucoside conjugation : In these reactions the harmful xenobiotics or their metabolites
combine with glucose to form conjugates. Most important reaction in insecticide
detoxification. Compounds with hydroxyl and carboxylic acid group undergo this.
iii). Amino acid conjugation : It occurs by the activation of the xenobiotic acid through the
enzyme requiring ATP and followed by condensation with endogenous amino acid.
iv). Acetylated conjugation : Compounds having amino or hydrazine are conjugated with
the help of acetyl coenzyme A.
v) Methylated conjugation : Compounds with amines and phenols exhibit this.
7. These are classified into 2 types:
A. Microsomal enzymes Phase 1 metabolism
• Microsomes are subcellular organelles found in cells. It contains various enzymes,
including cytochrome P450 enzymes (CYPs), responsible for catalyzing oxidative
reactions in the body.
Chemically, they are made up of lipoproteins and ribonucleic acid (RNA). Earlier,
microsomes were called "cytoplasmic basophilia’.
Examples are monoxygenases, Cytochrome P450, Epoxidase, Hydrolases etc.
B. Non microsomal enzymes Phase 2 metabolism
• These are present in the cytoplasm, mitochondria and in other tissues including
plasma. Ex: All conjugations except glucuronidation are carried out by Non-microsomal
enzymes.
8. Phase 1 reactions are mainly catalyzed by the cytochrome P450 group of enzymes.
Phase 1 reactions include, Microsomal oxidation.
The NADPH-requiring general oxidation system, commonly referred to as the
“Microsomal oxidase system” (also known as monooxygenase or mixed function
oxidase, MFO).
The monooxygenase system gets its name from the way the atoms from the oxygen
molecules are separated from one another and end up in different substances.
(i.e, one oxygen molecule gets inserted into an appropriate substrate, R-H. The other
oxygen atom eventually produces a water molecule)
R-H + O₂ + [2H] R-OH + H₂O
& the Term ‘Mixed function oxidase’ refers to the enzyme function to oxidize two
separate substrates at the same time.
9. MFOs are characterized by the oxidization of many different kinds of substrates.
The major components of the MFOs are:
A. NADPH-cytochrome c reductase, Flavoprotein, (as a cofactor)
It is a mediator of electron flow from NADPH to the oxygen activating enzyme.
It has 2 moles of FAD (flavin adenine dinucleotide) per mole.
B. Cytochrome P450 (electron transport system)
It is the common oxygen-activating enzyme for the entire family of microsomal mixed function
oxidases.
These are actually hemoprotein of b cytochrome type.
Iron in reduced state can bind with high affinity to carbon monoxide and this CO-bound CYP
complex shows a large absorbance at 450nm.
10. • CYPs contains the main group of enzymes for Phase I metabolism.
• The oxidizing sites in these enzymes is the heme centre and is responsible for the
oxidation of hydrophobic compounds to hydrophilic metabolites for excretion.
• It catalyze the transfer of one atom of oxygen to a substrate producing an oxidized
substrate along with a molecule of water, as given below,
11. The process of microsomal oxidation integrates the transfer of electrons from NADPH with
the binding of substrate and oxygen at CYP450.
Two separate one-electron reductions are involved i.e, the first occurs with the substrate-
oxidized CYP450 complex and the second with the reduced cytochrome
P450/substrate/oxygen complex.
Subsequently to catalysis, oxidized CYP450 is regenerated by dissociation of the hydroxylated
product and water.
The mechanism of microsomal oxidation involves three basic events
i. Substrate binding
ii. Reduction &
iii. Oxygen binding and activation.
Catalytic Events of Microsomal
Oxidase System
13. i) Substrate binding :
Here, the electrons from NADPH integrate the of substrate and oxygen at CYP450.
ii) Reduction :
It occurs in two separate one-electron steps due to the transfer of electrons from NADPH to CYP450.
a) Reduction of CYP450-substrate complex via NADPH-cytochrome c reductase (in the presence of
carbon monoxide with peak absorbance at 450 nm.
b) The second electron is introduced at the OxyCYP450-substrate complex.
iii) Oxygen binding and Activation:
Binding of carbon monoxide to cytochrome in competition with oxygen indicates the role of
cytochrome in oxygen activation.
So, the oxygen molecule is activated and split, one atom being inserted into the substrate and
the other reduced to water.
14. Most organic insecticides and synergists are subject to
microsomal oxidation
Many of them possess multiple sites at which oxidation
can occur.
Oxidative transformation of insecticides will be
discussed in five categories:
1. O-, S-, and N- Alkyl Hydroxylation
2. Desulfuration
3. Epoxidation
4. Thio ester oxidation
5. Aromatic hydroxylation Examples of multiple sites for
microsomal oxidation
Microsomal Oxidation of
Insecticides
15. Here, an alkyl group adjacent to a hetero atom such as
oxygen, sulfur, and or nitrogen is a potential target for
microsomal hydroxylation.
But because of the electronegativity of the hetero-
atom, the reaction often leads to dealkylation.
O- dealkylation
Dealkylation of O-alkyl groups of ester or ether
containing insecticides occurs readily.
First an unstable hydroxyl intermediate is produced
which spontaneously releases an aldehyde in the case
of a primary alkyl group or a ketone in the case of a
secondary alkyl group .
phorate
1. O-, N-, and S-
Dealkylation
O- dealkylation
16. S- dealkylation
S- demethylation of several ethylthio compounds has been
reported, and its involvement in phorate metabolism leads
to conversion of the methyl thiocarbon to carbondioxide.
N- dealkylation
Occurs in the metabolism of many organophosphates and
carbamates.
This reaction often yields a fairly stable N-hydroxy alkyl
derivative, probably because nitrogen is less electronegative
than oxygen.
The metabolite then may undergo non-oxidative cleavage to
a dealkylated product and an aldehyde.
S- dealkylation
18. 2. Desulfuration
Desulfuration is one of the most common metabolic pathway of organophosphorus insecticides
which contains phosphorothioate and phosphorodithioate esters.
P S structure of organophosphorus insecticides are desulfurated to their corresponding P
O analogues by microsomal oxidases.
The detached sulfur is eventually excreted as inorganic sulfate.
Oxidative desulfuration of P=S P=O is always lead to more toxic products.
(phosphorothioate activation to phosphate).
The formation of oxons require NADPH and molecular oxygen
20. 3. Thioether or Sulfur Oxidation
Sulfoxidation of phorate or aldicarb, where one atom
of oxygen is attached with S, forming sulfuroxide and
when two atoms of oxygen are attached with S,
forming sulfone.
Enzyme responsible in this reaction is called
sulfoxidase.
Usually, the alkyl sulfur in insecticide is rapidly oxidized
to sulfoxide and more slowly to sulfones.
Recently, it was observed that these sulfoxides enter
into phase 2 reaction, where they conjugate with
glutathione and finally excreted from body.
21. 4. Aromatic hydroxylation
or NIF shift
The NIF shift (named after the National
Institute of Health, where it was discovered) is
a characteristic of aromatic hydroxylation by all
mixed function oxidases.
During such hydroxylation reactions, the
hydrogen atom replaced by the hydroxyl group
is not always expelled from the molecule, but
may migrate to an adjacent position in the ring.
The degree of hydrogen retention varies with
different substrates.
22. 5.
Epoxidatio
n
Stable and environmentally persistant epoxides of
dihydrodiols are formed.
Enzymes epoxidase catalyzes these reactions to
form dihydrodiols.
Important degradation reaction in case of
cyclodiene compounds e.g., heptachlor, aldrin.
When this reaction occurs, the oxygen gets
detached to the place where chlorine is absent, but
double bond is present.
These epoxides may further go for hydroxylation
and form trans-diols.
23. • The Toxicology and Biochemistry of Insecticides. 2015. Simon J. Yu.
• Applied Entomology Toxicology of Insecticides. 2007. Dileep K. Singh.
Referen
ces
NADPH-cytochrome c reductase is recognized as a mediator of electron flow from NADPH to the oxygen-activating enzyme. A wide variety of chemicals are enzymatically oxidized by this microsomal system in the prese:nce of molecular oxygen and NADPH
Many of them possess mUltiple sites at which oxidation can occur, and
consequently a combination of several transformations can take place with any
However, no S- demethylation of aldicarb has been detected in the rat liver in vitro system.
It is likely that the N-hydroxymethyl derivative is an intermediate in stepwise N-demethylation reactions of this compound.