Question

Why can't an enzyme have a $\frac{{\mathbf{k}}_{\mathbf{cat}}}{{\mathbf{K}}_{\mathbf{M}}}$ value greater than ${\mathbf{10}}^{\mathbf{9}}{\mathbf{M}}^{\mathbf{‐}\mathbf{1}}{\mathbf{s}}^{\mathbf{‐}\mathbf{1}}$?

Short answer

The $\frac{{\mathrm{k}}_{\mathrm{cat}}}{{\mathrm{K}}_{\mathrm{M}}}$value cannot be greater than ${10}^9{\mathrm{M}}^{‐1}{\mathrm{s}}^{‐1}$ because this value is near the diffusion-controlled limit.

Step-by-step solution

Introduction

Enzymes are biological catalysts that catalyze chemical reactions. These are proteins that minimize the activation energy required to initiate chemical reactions.

Enzyme has a greater value

This rate cannot be faster than the diffusion-controlled encounter of an enzyme and its substrate. No enzyme can have a diffusion limit greater than ${\mathbf{10}}^{\mathbf{9}}{\mathbf{M}}^{\mathbf{‐}\mathbf{1}}{\mathbf{s}}^{\mathbf{‐}\mathbf{1}}$, and this enzyme is working with maximum efficiency.

Thus, no enzyme can have $\frac{{\mathrm{k}}_{\mathrm{cat}}}{{\mathrm{K}}_{\mathrm{M}}}$ greater than the value ${10}^9{\mathrm{M}}^{‐1}{\mathrm{s}}^{‐1}$.