Biocatalyst that increase the rate of biochemical reaction.

1. ENZYMES- CLASSIFICATION,
MECHANISM AND KINETICS
S.P.R VISHALI
I M. Sc. Biotechnlogy
PG & Research department of Biotechnology and Microbiology
National College (Autonous), Trichy, Tamil Nadu

2. CONTENTS

3. • Enzyme - Biocatalyst that increase the rate of biochemical
reaction.
• All enzymes are protein but all proteins are not enzymes.
• Except
• Highly specific.
• It increases the rate of reaction by lowering activation energy.
• Do not change the equilibrium state of biochemical energy.

4. ENZYME
RNA
(Ribozyme)
PROTEIN
CONJUGATED
ENZYME
SIMPLE
ENZYME

5. NON-PROTEIN
(Cofator)
COENZYME
(Organic compound)
METAL ION
PROTEIN
(Apoenzyme)
CONJUGATED
ENZYME

6. COENZYME
(Organic compound)
METAL ION
COSUBSTRATE
(Loosely bound)
PROSTHETIC
GROUP
(Tightly bound)
METALLOEN
ZYME
METAL
ACTIVATED

7. Enzymes have trivial name. i.e Named by adding suffix -ase
Substrate:
Activity:
Enzyme Commission has given all known enzymes a systematic
name and number in addition to its exsting trivial name.
 1st part - Substrate name
 2nd part - Nature of reaction. (ase)

8. • L-malate + NAD+ Pyruvate + CO2 +
NADH + H+
• Systematic Name :
CLASSIFICATION :
6 main classes of enzyme, on the basis of type of the
reaction catalyze.

10. EC NUMBER
• 1 - CLASS : Oxidoreductase
• 2 - SUBCLASS : Hydrogen or Electron donor (Alcohol,
Aldehyde, Amine etc)
• 3 - SUBSUBCLASS : Hydrogen or Electron acceptor (NAD+,
Fe3+, O2 etc)
• 4 - ORDER : The order in which each enzyme is added to the
list.
• Eg -

11. MECHANISM OF ENZYME ACTION
• An enzyme does not change the position of equilibrium in a
chemical reaction. It only accelerates the attainment of equilibria
but do not shift their positions.
• The formation of an ES complex is the step in enzymatic catalysis.
• Active Site - Catalytic and Binding sites.
• Substrate bind to active site by multiple weak noncovalent
interactions like hydrophobic interactions, H- bonds, ionic
interactions or reversible covalent bonds.
• Binding energy - The free energy released in the formation of a
large number of weak interaction between the enzyme and
substrate.

12. • Specificity of binding
depends on the precisely
defined arrangement of
atoms in the active site.
• Hydrogen bonding and
the shape of active site,
which rejects molecules
that do not have a
sufficient complementary
shape.

13. LOCK AND KEY MODEL
• Emil Fisher, 1894
• The active site of the
unbound enzyme is
complementary in shape
to the substrate.

14. INDUCED-FIT MODEL
• Daniel Koshland, 1958
• The enzymes changes
shape on substrate binding.
• The active site forms a
shape complementary to
the substrate only after the
substrate has been bound.

15. TRANSITION STATE
• Intermediary state of the
reaction.
• Unstable state and will
very quickly break down to
form the products.
• It is the point of highest
free energy, in whic the
substrates are partially
converted to products.

16. ACTIVATION ENERGY
• The difference in free
energy between the
transition - state and the
substrate is called Gibbs
free energy of activation or
simply the activation
energy, G+ .
• Greater the activation
energy, slower the reaction
rate

17. • Enzyme lowers the activation energy.
• Lowering of the activation energy occurs due to the binding
energy.
• Binding energy - Result of interactions between E&S.
• Only the correct substrate can form maximum interactions
with the enzyme and thus maximize the binding energy.

18. ENZYME KINETICS
• Study of rate of enzyme catalyzed reactions.
aA + bB Products
Rate α [A]a [B]b
Rate = K [A]a [B]b
• FIRST ORDER REACTION
Rate = k [A]1

19. • SECOND ORDER REACTION
Rate = k [A]1 [B]1
• ZERO ORDER REACTION
Rate = k [A]0 = k

20. • Rate depends on
the conc. of
substrate
• V0 - Initial velocity
• Vmax - Maximum
Velocity

21. MM Equation
• Leonor Michaelis and Maud L. Menten proposed a theory
of enzyme action in 1913.
• They proposed the single substrate enzyme catalyzed
reaction.
• K1 Rate constant for the formation of the ES Complex
• K-1 Dissociation of ES into E and S
• K2 Conversion of ES into product

23. ENZYME INHIBITION
• Enzyme inhibitor is a molecule that binds to an enzyme
and decreases its activity.
• The binding of an inhibitor can stop a substrate from
entering the enzyme's active site and/or hinder the enzyme
from catalyzing its reaction.
• Inhibitor binding is either reversible or irreversible.
• Reversible :
• Competitive Uncompetitive
• Mixed Non competitive

24. Irreversible
• Irreversible inhibitors
usually react with the
enzyme and change it
chemically (e.g. via
covalent bond formation).
• These inhibitors modify
key amino acid residues
needed for enzymatic
activity.
• Eg- All Drugs.

25. Reversible
• Reversible inhibitors bind non-covalently and different
types of inhibition are produced depending on whether
these inhibitors bind to the enzyme, the enzyme-
substrate complex, or both.
• Competitive: Substrate and Inhibitor competite for Active
site.
• Non Competitive: Enzyme has another region for
inhibitor binding - Allosteric site

27. Uncompetitive: Binds
with the ES Complex.

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