Enzymatic Synthesis of Plasmalogens

Abstract

Abstract Microsomes from the mucosa of hamster small intestine contain an enzyme system capable of catalyzing the desaturation of [3H]alkylacylglycerophosphorylethanolamine to form [3H]alk-1-enylacylglycerophosphorylethanolamine (ethanolamine plasmalogen). The enzyme is specific for 1-O-alkyl-2-acyl-sn-glycero-3-phosphorylethanolamine; it does not act on the enantiomeric 3-O-alkyl-2-acyl-sn-glycero-1-phosphorylethanolamine; 1-O-alkyl-sn-glycero-3-phosphorylethanolamine is utilized only after acylation in position 2 of the glycerol moiety; 1-O-alkyl-2-acyl-sn-glycero-3-phosphoryl-(N-dimethyl)ethanolamine is not converted to the corresponding plasmalogen; degradation products of alkyl- and alkylacylglycerophosphorylethanolamine, i.e. octadecylglycerol, octadecanal, octadecanol, or stearic acid are not utilized for plasmalogen biosynthesis by the in vitro system. The broad pH optimum of the reaction lies at pH 7 to 8. The alkylacylglycerophosphorylethanolamine desaturase requires as essential cofactors molecular oxygen, NADH, or NADPH and a heat-labile factor of high molecular weight contained in the 100,000 x g supernatant. Inhibition by cyanide indicates that a cyanide-sensitive factor is involved. The reaction is further inhibited by EDTA, NaN3, o-phenanthroline, p-chloromercuribenzoate, N-ethylmaleimide, menadione, and detergents, but not by carbon monoxide. As far as the type of reaction (cis-olefination), cofactor requirement, and susceptibility to the various inhibitors are concerned, alkylacylglycerophosphorylethanolamine desaturase resembles fatty acyl coenzyme A desaturase.