Exeristes,Itoplectis, Aphaereta,Brachymeria, and Hyposoter species: In vitro glyceride synthesis and regulation of fatty acid composition

Microsomes from two species of parasitic Hymenoptera, Exeristes roborator and Itoplectis conquisitor, exhibited little or no de novo glyceride synthesis but actively acylated endogenous mono- and diacylglycerides. It is suggested that this lack of de novo synthesis is related to the fact that the fatty acid composition of these parasitoid species closely resembles that of the hosts on which they are reared. Microsomes from three other species of parasitic Hymenoptera, Aphaereta pallipes, Brachymeria lasus, and Hyposoter exigua, whose fatty acid compositions are little influenced by the host species, exhibited active de novo glyceride synthesis as well as acylation of endogenous mono- and diacylglycerides. Radiotracer studies indicated that E. roborator microsomes and cytosol did not contain noncompetitive or uncompetitive inhibitors of glycerophosphate acyltransferase. E. roborator microsomes acylated exogenous phosphatidic acid but not dihydroxyacetone phosphate or glycerol. The maximum rate of glycerophosphate acylation was less than 0.1 nmole/min/mg microsomal protein after 15 min incubation. The incorporation was subject to rapid lipolysis on further incubation. The addition of bovine serum albumin (BSA) reduced the ability of E. roborator microsomes to acylate mono- and diacylglycerides with endogenous acyl groups. In the absence of BSA, palmitoyl-CoA was a more effective substrate than stearoyl-CoA for both mono- and diacylglyceride acyltransferases.