Question

4.4 For the enzyme reaction:

The Michaelis and Menten constant, Km is actually a summary of 3 terms:

(a) What are these? 

(b) What assumption does it make?

(c) Define and calculate  Km from the above equation given:

(d) Which is the rate-limiting step? And why?

Answer 1

At steady state,

Rate of formation of ES = Rate of break down of ES

K1[E] [S] = (K-1+K2) [ES]

[E] [S] / [ES] = (K-1 + K2) / K1 = Km = Michaelis menten constant

On substituting,

Km = (2+11) / 8

Km = 1.625

Since it is a constant there is no unit.

Note: the unit given for K1 should be sec-1 m-1. The given unit is a typo.

Km shows the binding affinity of a substrate towards the enzyme. It gives the concentration of the substrate [S] when Vo = 1/2 Vm. (Vo = reaction velocity and Vm is maximum velocity)