Inhibition of hydrocarbon biosynthesis in the housefly by 2-Octadecynoate

The elongation of 9,10-³H]oleoyl-CoA with malonyl-CoA to form 20, 22, and 24 carbon monounsaturated fatty acids was demonstrated in housefly microsomes by radio-GLC. These elongation reactions, which have been postulated to be involved in hydrocarbon biosynthesis, have not been previously demonstrated in insects. 2-Octadecynoate (18:1 Δ²⁼) inhibited the in vivo incorporation of 1-¹⁴C]acetate into both fatty acids and hydrocarbons in a dose-dependent manner. At doses of 10 μg per female housefly of the alkynoic acid, the incorporation of 1-¹⁴C]acetate into hydrocarbon was inhibited 93%, the incorporation of 9,10-³H]oleate into hydrocarbon was inhibited 64%, and the incorporation of 1-¹⁴C]acetate into total internal lipid was inhibited 65%. Partially purified FAS was inhibited 50% and 95% at 15 μM and 40 μM, respectively, of the alkynoic acid. These results show that 2-octadecynoate inhibits hydrocarbon biosynthesis in the housefly by inhibiting FAS, and the in vivo data suggest that the elongation of 18:1 to longer chain fatty acids is also inhibited.