Enzymes catalyze reactions by lowering the activation energy needed to reach the transition state. They provide an alternate reaction pathway with a lower energy barrier compared to uncatalyzed reactions. The active site of an enzyme chemically facilitates catalysis by stabilizing the transition state of the reaction. It acts as a flexible template that stabilizes the substrate in its transition state, accelerating the reaction. The active site also provides catalytic groups that increase the probability of transition state formation. Common mechanisms of enzyme action include the lock and key model and induced fit model. Enzyme catalysis is achieved through proximity effects, acid-base catalysis using functional groups to enhance transition state formation, substrate strain, and sometimes covalent catalysis where the

1. Enzyme
Kinetics
Prof. Dr. V.P. Acharya

2. How enzymes work???
 Enzymes provide an alternate,
energetically favorable pathway different
from uncatalyzed reaction
 The active site chemically facilitates
catalysis

3. A. Energy changes
occurring during reaction
A ↔ T* ↔ B
Energy barrier separates reactants
and products.
Energy barrier- Free energy of
activation
↓
Energy difference between reactants
and high energy intermediate T*

4. a) Free energy of activation
 Uncatalyzed reactions- high EA
 Rate of reactions thus slow

5. b) Rate of reaction
 For molecules to react they must possess
sufficient energy to overcome the barrier of
transition state
c) Alternate reaction pathway
Enzyme provides an alternate pathway having low
activation energy
Lowering of activation energy– making a tunnel in
the mountain

6. B. Chemistry of active site
1. 1. Transition state stabilization
Active site acts as a flexible molecular
template
↓
Stabilizes the substrate in its transition
state
↓
Reaction accelerated

7. 2.Providing catalytic group
Active site provides catalytic
groups
↓
↑ probability of transition state
formation
E+S↔ES ↔ E+ P

8. Visualization of the
transition state

10. Mechanism of enzyme action
 Michelis-Menten Theory
 Fischer’s template theory
 Koshland’s induced fit theory

12. Fisher’s Lock and Key
model

13. Koshland’s Induced fit model
Substrate induces conformational changes in enzyme

15. Man can accept his fate, man can

16. Mechanism of enzyme catalysis
1. Catalysis by proximity- reactants should
come closer
More reactants- ↑ probability of reaction due
to proximity (Entropy effect)
2. Acid-base catalysis- Ionizable functional
groups of amino-acyl side chains and
prosthetic groups act as acids & bases-
enhances formation of T state
a. Specific b. general

17. 3. Substrate strain
Enzyme binds to substrate in unfavorable way
↓
stretch or distortion of bond
↓
cleavage of bond
4. Covalent catalysis
Covalent bond between enzyme and one or more
substrates are formed
↓
Enzyme becomes a reactant
↓
On completion of reaction, enzyme returns to original state

18. Next class…………..
ENZYME KINETICS AND FACTORS
AFFECTING ENZYME ACTION

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