BIOSYNTHETIC ALTERNATIVES FOR ACETOGENIC PRODUCTION OF SORBIC ACID INTHE POTATO APHID (HOMOPTERA-APHIDIDAE)

Following in vivo injection of [1-C-14]-sodium acetate, triacylglycero ls of the potato aphid, Macrosiphum euphorbiae (Thomas), were extracte d and derivatized to p-bromophenacyl fatty acid esters for two-dimensi onal TLC and GLC-MSD (mass selective detector) analysis. Radiolabeled sorbic (E,E-2,4-hexadienoic) acid ester was detected, demonstrating th at this short chain fatty acid unique to aphids is biosynthesized via an acetogenic pathway. Crotonic (E-2-butenoic) or hexenoic acids were not detected in labeled or unlabeled potato aphid samples or unlabeled samples from the oleander aphid, Aphis nerii Fonscolombe. Crotonic or hexenoic acids might have been expected if an incomplete cycling by f atty acid synthetase or a novel desaturase acting on the prevalent hex anoate, respectively, were responsible for sorbic acid synthesis in ap hids. A peroxisomal beta-oxidation route to sorbic acid from longer ch ain fatty acids was not indicated since injections of clofibrate, a pe roxisomal proliferator, with or without C18 polyunsaturated lipids gav e no substantial increase in C6 lipids. Also, some characteristic enzy me activities of peroxisomal beta-oxidation were not found in an ultra centrifugal ''peroxisomal'' fraction from the potato aphid. Although t he individual biochemical steps from acetate to sorbate in aphids rema in unclear, an unusual acetate-malonate pathway is indicated. Clarific ation of the biosynthetic steps to sorbic acid should identify at leas t one novel enzyme for animals. (C) 1994 Wiley-Liss, Inc.