Kinetic studies on the reaction mechanism and the citrate activation of liver acetyl coenzyme A carboxylase.

Abstract

Kinetoc studies were carried out on the reaction mechanism of rat liver acetyl coenzyme A carboxylase. The results of initial velocity and product inhibition studies on the forward and reverse reaction indicate that the carboxylase reaction is most likely to proceed through the “bi bi uni uni ping pong” mechanism. The order of the addition of substrates to the enzyme is as follos: ATP, HCO3‐ and acetyl‐CoA in the forward reaction, and malonyl‐CoA, Pi and ADP in the reverse reaction.Kinetic analysis of the stimulatory effect of citrate on the initial velocities of the forward and reverse reaction indicate that the site of citrate action during catalysis lies predominantly onthe earboxylated enzyme. It is proposed that there exists and equilibrium between active and inactive forms of the carboxybiotinyl enzyme and that this equilibrium is shifted toward the active form in the presence of citrate.