Acetyl-CoA carboxylase catalyzes the first committed step in the synthesis of long-chain fatty acids. The Escherichia coli form of the enzyme consists of a biotin carboxylase protein, a biotin carboxyl carrier protein, and a carboxyltransferase protein. In this report, the synthesis of a bisubstrate analog inhibitor of carboxyltransferase is described. The inhibitor was synthesized by covalently linking biotin to coenzyme A via an acyl bridge between the sulfur of coenzyme A and the 1'-N of biotin. The steady-state kinetics of carboxyltransferase are characterized in the reverse direction, in which malonyl-CoA reacts with biocytin to form acetyl-CoA and carboxybiocytin. The inhibitor exhibited competitive inhibition versus malonyl-CoA and noncompetitive inhibition versus biocytin, with a slope inhibition constant (K-is) of 23 +/- 2 muM. The bisubstrate analog has an affinity for carboxyltransferase 350 times higher than biotin. This suggests the inhibitor will be useful in structural studies, as well as aid in the search for chemotherapeutic agents that target acetyl-CoA carboxylase. (C) 2002 Elsevier Science (USA).