Chapter 21, Problem 21.63QP

Interpretation Introduction

Interpretation:

The role of citrate in feedback inhibition of glycolysis has to be explained.

Concept Introduction:

The allosteric enzymes have an effector binding site other than the active site that binds substrate. These effector binding sites bind a chemical signal that can alter the rate of reaction, it is known as allosteric inhibition. Effector binding can increase as well as decrease the rate of reaction.

The feedback regulation can be understood from the synthetic pathway given as follows:

  $\text{A}\stackrel{{\text{E}}_{\text{1}}}{\to }\text{B}\stackrel{{\text{E}}_{\text{2}}}{\to }\text{C}\stackrel{{\text{E}}_{\text{3}}}{\to }\text{D}\stackrel{{\text{E}}_{\text{4}}}{\to }\text{E}\stackrel{{\text{E}}_{\text{5}}}{\to }\text{F}$

When the concentration of the final product F exceeds the desired concentration than the cycle is automatically shut off. So, here the product $\text{F}$ serves as the negative allosteric effector for the enzymes that start this synthetic pathway. Consequently, the activity of the enzyme ${\text{E}}_{\text{1}}$ is inhibited. With the inactivation of this enzyme that is required in the first of the synthetic steps the entire sequence of reaction ceases.