Chemical B.tech 3rd year
Enzymes: proteins that function as biological catalysts.
Catalyst: a substance that speeds up a chemical reaction and
is not changed by the reaction.
Specificity:Enzymes are usually very specific as to
Which reaction they catalyze.
Highly specific Enzymes follows "proof-reading"
“Lock and key” model
However certain substances can bind to the enzyme at sites other than the
Active site and modify its activity (inhibitors/co-factors)
Idea that the enzyme is flexible.
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
enzyme + productenzyme-substrate complex
enzyme + substrate enzyme-substrate complex
E +S ES
Enzymes can act in several ways, all of which lower ΔG‡
• Lowering the activation energy by creating an
environment in which the transition state is stabilized
• Lowering the energy of the transition state, but
without distorting the substrate.
• Providing an alternative pathway.
• Reducing the reaction entropy change by bringing
substrates together in the correct orientation to
0 20 30 5010 40 60
40oC - denatures
Increase in Activity
<5oC - inactive
Effect of heat on enzyme activty
If you heat the protein above its optimal temperature
meaning the protein loses it secondary and tertiary structure
Effect of heat on enzyme activty
Denaturing the protein
Effect of heat on enzyme activty
Denaturing the protein
ACTIVE SITE CHANGES SHAPE
SO SUBSTRATE NO LONGER FITS
Even if temperature lowered – enzyme can’t regain its correct shape
• The ph scale measures how acidic or alkaline a
• The chemical properties of many solutions enable
them to be divided into 3 categories:
1) Neutral: solutions with a ph of 7.
2) Alkaline: solutions with a ph greater than 7
3) Acidic: solutions with a ph less than 7.
Active sites full- maximum turnover
• Metabolism is the sum of all biochemical
reactions occurring in living cells.
• These reactions can be divided into two main
– 1) ANABOLISM
– 2) CATABOLISM
• Involves the synthesis
of complex molecules
from simpler molecules
which requires energy
• Involves the breakdown
of complex molecules
into simpler molecules
involving hydrolysis or
oxidation and the
release of energy.
• Energy releasing processes, ones that
"generate" energy, are termed exergonic
• Reactions that require energy to initiate the
reaction are known as endergonic reactions.
• All natural processes tend to proceed in such a
direction that the disorder or randomness of
the universe increases
• This kind of reaction is not termed a
spontaneous reaction. In order to go from
the initial state to the final state a
considerable amount of energy must be
imparted to the system.
• These kinds of reactions are associated with
a positive number (+G).
• The speed V means the number of reactions per
second that are catalyzed by an enzyme.
• With increasing substrate concentration [S], the
enzyme is asymptotically approaching its maximum
speed Vmax, but never actually reaching it.
• Because of that, no [S] for Vmax can be given.
• Instead, the characteristic value for the enzyme is
defined by the substrate concentration at its half-
maximum speed (Vmax/2).
• This KM value is also called Michaelis-Menten
Vo = Vmax
• Vo = Initial reaction velocity
• Vmax = Maximum velocity
• Km = Michaelis constant
• [S] = Substrate concentration
It is widely used. It takes into account the name of the
substrate of the enzyme and the type of catalyzed reaction. To
designate an enzyme is indicated:
the name of the first substrate
then the type of reaction catalyzed
Finally we add the suffix ase.
- Glucose-6-phosphate isomerase
- Isocitrate lyase
- Pyruvate carboxylase
When the enzyme uses two substrates and are described
by specifying both
radicals of the donor substrate
the acceptor substrate and then released the radical
exchanged the radical
the type of reaction
finally added ase
- ATP-glucose phosphotransferase
- UDPglucose-fructose glucosyltransferase
- Glutamate pyruvate transaminase
Enzyme Nomenclature official
1: oxidoreductases, which catalyze electron transfer
2: The transferases, which catalyze the transfer of groups
3: hydrolases which catalyze hydrolysis reactions
4: lyases, which catalyze the addition of groups to double
bonds or vice versa
5: isomerases which catalyze the transfer of groups in one
molecule to produce isomeric forms (the conversion of an
amino acid D-amino acid in L 'for example)
6: ligases, which form links CC, CS, CN and CO during
condensation reactions coupled with the use of ATP.
The different types of enzymes:
• 4.1 - of redox enzymes and oxygen fixation
• 4.1.1 - dehydrogenation of the alcohol,
• 4.1.2 - dehydrogenases appear by double
• 4.1.3 - dehydrogenases acting on functions
• 4.1.4 - enzymes involved in the transfer of
electrons in the mitochondria
• 4.1.5 - oxygenases
• 4.2 - transferases
• 4.2.1 - enzymes transferring a methyl group
• 4.2.2 - the transferring enzymes radicals has
• 4.2.3 - the transferring enzymes of
• 4.2.4 - aminotransferases
• 4.2.5 - Phosphotransferases
• 4.3 - hydrolases
• 4.3.1 - carbohydrate hydrolases
• 4.3.2 - hydrolases phosphoric esters of
4.3.3 lipid hydrolases
4.3.4 - hydrolases of peptides and proteins
4.3.5 - hydrolases nucleosides, nucleotides and
4.3.6 - hydrolase esters or phosphoric anhydride
4.4 - lyases and synthases
4.4.1 - decarboxylases
4.4.2 - aldehyde-lyases
4.4.3 - acyl-lyase or acylsynthase
4.4.4 - hydratases and dehydratases
4.5 - isomerases
4.5.1 - epimerization
4.5.2 - intramolecular redox
4.5.3 - transport of radicals
4.6 - ligases (synthetases)
4.6.1 - forming links ligases c-o
4.6.2 - bond forming ligase c-c
4.6.3 - links ligases c-s
4.6.4 - links ligases c-n
• A non protein component of enzymes is called the
• If the cofactor is organic, then it is called a coenzyme.
• Coenzymes are relatively small molecules compared to
the protein part of the enzyme.
• Many of the coenzymes are derived from vitamins.
• The coenzymes make up a part of the active site, since
without the coenzyme, the enzyme will not function.
• In the graphic on the left is the structure for the
coenzyme, NAD+, Nicotinamide Adenine
• Nicotinamide is from the niacin vitamin.
• The NAD+ coenzyme is involved with many types
of oxidation reactions where alcohols are
converted to ketones or aldehydes.
Vitamin Coenzyme Function
coenzyme A (CoA) Acetyl group carrier
vitamin B-12 coenzyme B-12
• Coenzyme Q10 is a fat-soluble nutrient also known as
CoQ10, vitamin Q10, ubidecarenone, or ubiquinone.
• It is a natural product of the human body that is
primarily found in the mitochondria, which are the
cellular organelles that produce energy.
• It occurs in most tissues of the human body; however,
the highest concentrations are found in the heart, liver,
kidneys, and pancreas.
• Ubiquinone takes its name from a combination of the
word ubiquitous, meaning something that is found
everywhere, and quinone 10.
• Quinones are substances found in all plants
• The variety found in humans has a 10-unit
side chain in its molecular structure.
• Apart from the important process that
provides energy, CoQ10 also stabilizes cell
membranes and acts as an antioxidant.
• In this capacity, it destroys free radicals, which
are unstable molecules that can damage
• Enzyme inhibitors are molecules that interact in
some way with the enzyme to prevent it from
working in the normal manner.
• There are a variety of types of inhibitors
including: nonspecific, irreversible, reversible -
competitive and noncompetitive.
• Poisons and drugs are examples of enzyme
• A nonspecific inhibition effects all enzymes in
the same way.
• Non-specific methods of inhibition include any
physical or chemical changes which ultimately
denatures the protein portion of the enzyme
and are therefore irreversible.
Non Specific Inhibitor
• Temperature: Usually, the reaction rate increases
with temperature, but with enzyme reactions, a
point is reached when the reaction rate
decreases with increasing temperature.
• At high temperatures the protein part of the
enzyme begins to denature, thus inhibiting the
• A competitive inhibitor is any compound
which closely resembles the chemical
structure and molecular geometry of the
• The inhibitor competes for the same active
site as the substrate molecule.
• The inhibitor may interact with the enzyme at
the active site, but no reaction takes place.
• The inhibitor is "stuck" on the enzyme and prevents
any substrate molecules from reacting with the
• However, a competitive inhibition is usually
reversible if sufficient substrate molecules are
available to ultimately displace the inhibitor.
• Therefore, the amount of enzyme inhibition depends
upon the inhibitor concentration, substrate
concentration, and the relative affinities of the
inhibitor and substrate for the active site.
• A noncompetitive inhibitor is a substance that forms
strong covalent bonds with an enzyme and
consequently may not be displaced by the addition
of excess substrate.
• Therefore, noncompetitive inhibition is irreversible.
• A noncompetitive inhibitor may be bonded at, near,
or remote from the active site. In any case, the basic
structure of the enzyme is modified to the degree
that it ceases to work.
• If the inhibition is at a place remote from the
active site, this is called allosteric inhibition.
• Allosteric means "other site" or "other
• The interaction of an inhibitor at an allosteric
site changes the structure of the enzyme so
that the active site is also changed.
• There are approximately 3000 enzymes which
have been characterised.
• These are grouped into six main classes
according to the type of reaction catalysed.
• At present, only a limited number are used in
enzyme electrodes or for other analytical
• These enzymes catalyse oxidation and
reduction reactions involving the transfer of
hydrogen atoms or electrons.
• The following are of particular importance in
the design of enzyme electrodes.
• This group can be further divided into 4 main
– catalyse hydrogen transfer from the substrate to
molecular oxygen producing hydrogen peroxide as
a by-product. An example of this is FAD
dependent glucose oxidase which catalyses the
– b-D-glucose + O2 = gluconolactone + H2O2
– catalyse hydrogen transfer from the substrate to a
nicotinamide adenine dinucleotide cofactor
(NAD+). An example of this is lactate
dehydrogenase which catalyses the following
– Lactate + NAD+ = Pyruvate + NADH + H+
– catalyse oxidation of a substrate by hydrogen
– An example of this type of enzyme is horseradish
peroxidase which catalyses the oxidation of a number
of different reducing substances (dyes, amines,
hydroquinones etc.) and the concomitant reduction
of hydrogen peroxide.
– The reaction below illustrates the oxidation of neutral
ferrocene to ferricinium in the presence of hydrogen
– 2[Fe(Cp)2] + H2O2 + 2H+= 2[Fe(Cp)2]+ + 2 H2O
– catalyse substrate oxidation by molecular oxygen.
– The reduced product of the reaction in this case is
water and not hydrogen peroxide.
– An example of this is the oxidation of lactate to
acetate catalysed by lactate-2-monooxygenase.
– lactate + O2 = acetate + CO2 + H2O
• These enzymes transfer C, N, P or S containing
groups (alkyl, acyl, aldehyde, amino,
phosphate or glucosyl) from one substrate to
• Transaminases, transketolases, transaldolases
and transmethylases belong to this group.
• These enzymes catalyse cleavage reactions or
the reverse fragment condensations.
• According to the type of bond cleaved, a
distinction is made between peptidases,
esterases, lipases, glycosidases, phosphatases
and so on.
• Examples of this class of enzyme include;
cholesterol esterase, alkaline phosphatase and
• These enzymes non-hydrolytically remove
groups from their substrates with the
concomitant formation of double bonds or
alternatively add new groups across double
• These enzymes catalyse intramolecular
rearrangements and are subdivided into;
• An example of this class of enzyme is glucose
isomerase which catalyses the isomerisation
of glucose to fructose.
• Ligases split C-C, C-O, C-N, C-S and C-halogen bonds
without hydrolysis or oxidation.
• The reaction is usually accompanied by the
consumption of a high energy compound such as ATP
and other nucleoside triphosphates.
• An example of this type of enzyme is pyruvate
carboxylase which catalyses the following reaction:
• pyruvate + HCO3- + ATP = Oxaloacetate + ADP + Pi