FATTY-ACID ELONGATION IN THE BIOSYNTHESIS OF (Z)-10-HEPTADECEN-2-ONE AND 2-TRIDECANONE IN EJACULATORY BULB MICROSOMES OF DROSOPHILA-BUZZATII

A fatty acid chain elongation process is involved in incorporation of saturated and unsaturated fatty acyl-CoA esters into 2-tridecanone and (Z)-10-heptadecen-2-one by Drosophila buzzatii. The microsomal fracti on from mature male ejaculatory bulbs is chain-length specific and req uires malonyl-CoA (or acetyl-CoA, if acetyl-CoA carboxylase were prese nt) for the chain elongation step to 2-ketones. Decarboxylation of the proposed intermediate beta-ketoacid results in 2-ketone biosynthesis. Incubation of the microsomes with the acetyl-CoA carboxylase inhibito r avidin indicated that acetyl-CoA carboxylase was present in the micr osomal preparations; however, washing of the microsomal preparation re moved the acetyl-CoA carboxylase activity. Fatty acyl-CoA esters were also chain elongated to produce fatty acids two and four carbons longe r, suggesting that the enzymes for normal fatty acid chain elongation are also present in the microsomal fraction from ejaculatory bulbs. Ho w much, if any, of this fatty acid chain elongation system is used for 2-ketone biosynthesis is yet to be determined.