Tissue and chain length specificity of the fatty acyl-CoA elongation system in the American cockroach

The elongation of fatty acyl-CoAs, reactions involved in hydrocarbon biosynthesis, was examined in the cockroach, Periplaneta americana. Products were analyzed by radio-HPLC and radio-GLC. The majority of the elongation activity was observed in microsomes prepared from abdominal epidermal tissue. Linoleoyl-CoA (18:2-CoA) was elongated most efficiently followed by stearoyl-CoA (18:0-CoA), linolenoyl-CoA (18:3-CoA; n-3) and oleoyl-CoA (18:1-CoA). The products of 18:2-CoA elongation included all even numbered acyl groups up to 28 carbons, and the products of 18:0-CoA included all even numbered acyl groups to 26 carbons. The 18:3-CoA was elongated only to 20 and 22 carbons. Radioactivity from both 18:2-CoA (5.4%) and 18:0-CoA (1.2%) was recovered in the hydrocarbon fraction. Analysis of this hydrocarbon fraction showed that the radio-activity from 18:2-CoA was present in (Z,Z)-6,9-heptacosadiene and that the radioactivity from 18:0-CoA was present in n-pentacosane. These data demonstrate for the first time in an in vitro insect system that the fatty acid elongation reactions are coupled with the conversion of the elongated product to hydrocarbon. Thus, each of the expected intermediates in the conversion of 18:0 and 18:2 to 25 and 27 carbon hydrocarbons, respectively, was observed, and the results demonstrate high tissue, substrate, and product specificity.