Acetyl-CoA carboxylase catalyzes the first committed step in fatty acid synthesis. In
Escherichia coli, the enzyme is composed of three distinct protein components: biotin
carboxylase, biotin carboxyl carrier protein, and carboxyltransferase. The biotin carboxylase
component has served for many years as a paradigm for mechanistic studies devoted
toward understanding more complicated biotin-dependent carboxylases. The three-
dimensional x-ray structure of an unliganded form of E. coli biotin carboxylase was originally …