The Enzymic Synthesis of Ethanolamine Plasmalogens

Abstract

Abstract Enzymic synthesis of ethanolamine plasmalogens from 1-14C-hexadecanol in cell-free systems from Ehrlich ascites and preputial gland tumors of mice is documented. Identification of the ethanolamine plasmalogens is based on the preparation and chromatographic behavior of a number of chemical derivatives that take into account all three positions on the glycerol moiety. 14C-Derivatives isolated from intact ethanolamine plasmalogens included (a) hexadecanal liberated by aqueous HCl, (b) dimethylacetals of hexadecanal formed by HCl-methanol treatment, (c) O-alk-1-enylglycerols liberated by reduction with LiAlH4 or NaAlH2(OCH2CH2·OCH3)2, (d) O-alkylglycerols obtained by hydrogenation of O-alk-1-enylglycerols, (e) isopropylidene derivatives of the hydrogenated O-alk-1-enylglycerols, (f) lysoethanolamine plasmalogens after phospholipase A treatment, and (g) dinitrobenzene derivatives of the intact ethanolamine plasmalogens. NaAlH2(OCH2CH2OCH3)2, a new reagent that we used for the reduction of ether-linked glycerolipids, gives better yields of O-alk-1-enylglycerols than LiAlH4. The system used for plasmalogen biosynthesis contained fatty alcohol, dihydroxyacetone phosphate, ATP, coenzyme A, Mg++, NADP+ or NAD+, microsomes, and the soluble fraction from tumors. Soluble fraction from rat liver can replace the soluble fraction from tumors. Data obtained with U-14C-labeled dihydroxyacetone phosphate and 9,10-3H-hexadecanol demonstrated that the 3H:14C ratios in O-alkylglycerols and O-alk-1-enylglycerols (isolated after LiAlH4 reduction) were essentially identical. 1-14C-Palmitic acid was not incorporated into the O-alk-1-enyl moiety and added unlabeled hexadecanal had little effect on plasmalogen biosynthesis. These data, along with the substrate and cofactor requirements, suggest that an O-alkyl glycerolipid was converted to an ethanolamine plasmalogen.