1. Enzyme kinetics -- Michaelis Menten kinetics
Two approaches:
Rapid equilibrium approach
Quasi steady state approach
Assumptions:
Total enzyme concentration remains constant during the reaction
Amount of enzyme is very small compared to amount of substrate
The product concentration is so low that the product inhibition is negligible.

2. where
k1= forward rate constant for formation of ES complex
k2= backward rate constant for formation of ES complex
k3= rate constant for formation of product P

3. some notations…….. e = concentration of enzyme
s = concentration of substrate
p = concentration of product
(es) = concentration of enzyme substrate complex
t = time
v = reaction rate or velocity

4. Michaelis Menten kinetics --Rapid equilibrium approach
It is assumed that ES complex is established very rapidly (since this equilibrium step is only the formation of weak interaction between E & S)
The product releasing step (k3) is very slow…….which determines the rate
The rate of reverse reaction of the second step is negligible

5. The equilibrium constant
The rate of product formation, (mol/ l.s)
The total enzyme concentration 1 2 3

6. Get an expression for (es) in known quantities……
Sub. eqn (1) in (3)

7. Now sub. the value of (es) in eqn 2.
Michaelis Menten Equation 5

8. Three special cases…….. Case I (s=KM) Therefore……..
is a function of enzyme concentration only
A low value of means that the enzyme has high affinity for the substrate
Three special cases……..
Case I (s=KM)
Case II (s>>KM)
Case III (s<<KM)

9. Case I (s=KM) Eqn. (5) =>
So when s=KM, the rate of reaction is one half of its maximal value.
i.e. at which 50% of enzyme active sites are occupied by substrate

10. Case II (s>>KM)
Eqn. (5) =>
 ZERO ORDER

11. Case III (s<<KM)
Eqn. (5) =>
FIRST ORDER

13. Michaelis Menten kinetics --Quasi steady state approach
This approach is assumed that the change in the intermediate (transition complex) concentration with respect to time is negligible. (pseudo steady state/quasi steady state)---
Briggs-Haldane approach
i.e.

14. 1 1 1

15. By p.s.s assumption,
Eqn 4==>

16. We know,

17. sub the value of (es) in (1)
Michaelis Menten Equation

18. Means that ‘S’ is costant…..which is not correct
Controversy of Equilibrium approach:
by Equilibrium approach,
Means that ‘S’ is costant…..which is not correct

19. This has been rectified by PSS approach…..
by PSS assumption

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