Catalysis of Water Oxygen and of Acetate Incorporation into Fatty Acids by Escherichia coli Fatty Acid Synthetase

Abstract

During synthesis of long chain fatty acids by an Escherichia coli fatty acid synthetase preparation in the presence of acyl carrier protein (ACP), fatty acyl-ACP is cleaved. The cleavage in H18OH resulted in the incorporation of about 1.7 atoms of water oxygen into each molecule of fatty acid synthesized. A portion of these water oxygens entered the fatty acid as a result of an exchange reaction. Addition of acetate and malonate decreased the number of water oxygens incorporated per fatty acid synthesized to 1.2 and inhibited the exchange of oxygen between the fatty acid carboxyl group and water. Free acetate and to a much lesser extent free malonate were incorporated into fatty acid. The synthesis of fatty acid and the incorporation of acetate were differentially inhibited by high levels of ACP fraction. No transfer of oxygen from the carboxyl group of acetate to the carboxyl group of long chain fatty acids was noted. These data support the proposal that fatty acyl-ACP is hydrolytically cleaved by the E. coli fatty acid synthetase preparation. The hydrolysis reaction was not rate-limiting as shown by the lack of detectable fatty acyl-ACP levels at any time during the course of the incubation.