Question

A combination of KM and kcat with which relative values is indicative of the lowest catalytic efficiency for an enzymatically catalyzed reaction?
a. A high Km and a low kcat
b. A high Km and a high kcat
c. A low Km and a high kcat
d. A low Km and a low kcat

Answer 1

Answer:

option a

Explanation:

$k_{cat}$ is turnover number. The turnover number is defined as the number of chemical conversions by single enzymatic site per second.

K_m is Michaelis-Menten constant used in the study of kinetics of enzyme catalyzed reaction.

The relationship between Michaelis-Menten constant and turnover number is as follows:

$v=k_{cat}[E_0]\frac{[S]}{K_m+[S]}$

Here, [S] is substrate concentration, E0 is the initial enzyme concentration and v is the rate of enzyme catalyzed reaction.

Turn over no. ($k_{cat}$) is present in nominator while K_m is present in denominator. Therefore for lowest catalytic efficiency, turnover ( $k_{cat}$) should be low and Michaelis-Menten constant (K_m) should be high.

Therefore, among, given option a is correct.