Question

What do the following kinetic parameters measure in enzyme reactions? a) KM b) kcat c) kcat/KM

How do you know you are at the “steady state” (measuring initial velocities) when studying an enzyme reaction?

Answer 1

KM, the Michaelis-Menten constant is the ability of an enzyme to bind to the substrate. Lesser value of Km indicate more affinity of an eznyme to the substrate. It can also be defined as substrate concentration at which the rate is Vmax/2.

Kcat = Vmax/Et, Et= total enzyme concentration.

From Michaelis-Menten equation

V= VmaxS/(KM+S)

when S<<< KM

V= VmaxS/KM

V= Kcat*S

so it is the proportionality constant between the rate and substrate concentration.

Kcal is also called as turn over number and is defined as the rate constant when the substrate concentration is negligible. It is the catalytic efficiency of an enzyme.

the Mechanism of Enzyme kinetics involves

E+S ---->ES----->P

steady state conditions refer to a state where the concentration of substrate bound enzyme (ES) changes so slowly   the net rate of ES can be considered as zero.

d/dt(ES)= 0