Acetyl coenzyme A carboxylase.

Abstract

Publisher Summary This chapter discusses the molecular properties of acetyl-CoA carboxylases from animal, bacterial, and plant cells. It also focuses on the regulation of catalytic activity. The mode of regulation of acetyl-CoA carboxylase reflects its physiological role in animal and bacterial cells. The carboxylase reaction, being the first committed step of the major energy storage pathway in animals, is regulated through feed-forward activation, while the E. coli enzyme, being catalyst for the initial step of a biosynthetic pathway involved in membrane synthesis, is regulated by the inhibitory action of a growth modulator. The carboxylases from both animal and bacterial sources possess two catalytic sites: (1) a biotin carboxylase site at which the biotin prosthetic group is carboxylated, and (2) a carboxyl transferase site at which the carboxyl group is transferred to acetyl-CoA to form malonyl-CoA. Regulation of the animal acetyl-CoA carboxylases by the feed-forward allosteric activator, citrate, appears to be mediated through a conformational change that perfects the orientation of the biotin prosthetic group with respect to both catalytic sites. The regulation of the bacterial enzyme is exerted through the inhibitory action of ppGpp, a growth modulator, on the carboxyl transferase component of the acetyl-CoA carboxylase system.