Acetyl-CoA-dependent chain elongation of fatty acids in Escherichia coli K-12

Crude extract of Escherichia coli was found to elongate medium chain acyl-CoA primers. The reaction products were fatty acids one or two C2 units longer than the primer. Acetyl-CoA acted as the condensing unit in this reaction, while malonyl-CoA did not. The optimal pH for the reaction was 5.0 in 0.1 M citrate-phosphate buffer. NADH was the predominant electron donor for the incorporation of acetyl-CoA into fatty acids, and NADPH was one-third as effective as NADH at pH 5.0. Acyl carrier protein and cerulenin had no effect on the acetyl-CoA incorporation into the chain elongation products. Acyl-CoA compounds with medium carbon chain lengths proved to be the best as primers, and the maximum incorporation was observed with octanoyl-CoA. N-Ethylmaleimide and p-hydroxymercuribenzoate blocked the chain elongation reaction by inhibiting either condensation or 3-ketoacyl reduction.