Question

1. What happens to the rate of the citric acid cycle in the presence of a respiratory uncoupler? Explain why this happens on the basis of enzyme regulation.

Answer 1

An uncoupler is an agent that dissociates two integrated series of chemical reactions especially: one that prevents the formation of ATP in oxidative phosphorylation in mitochondria by dissociating the reactions of phosphorylation from those concerned with electron transport and oxidation. Thus an uncoupled do not affect electron transport chain and ATP synthase.

Now ATP is an allosteric inhibitor of citrate synthase. The effect of ATP is to increase the value of K_M for acetyl CoA. Thus, as the level of ATP increases, less of this enzyme is saturated with acetyl CoA and so less citrate is formed. Thus in the presence of an uncoupler, there is low ATP and hence Citric acid cycle is not inhibited and it continues continuously.