The Metabolism of Glyceride Glycolipids

Abstract

Abstract Particulate enzyme preparations of Streptococcus faecalis ATCC 9790 catalyze the synthesis of 1,2-di-O-acyl-3-O-(α-d-glucopyranosyl)-sn-glycerol (monoglucosyl diglyceride), 1,2-di-O-acyl-3-O-(2-O-α-d-glucopyranosyl-α-d-glucopyranosyl)-sn-glycerol (diglucosyl diglyceride), and a third glucolipid of unknown structure from two common precursors, UDP-glucose and 1,2-diglyceride. The three glucolipids appear to be formed sequentially. Isolated, radiochemically pure monoglucosyl diglyceride is converted to diglucosyl diglyceride in a reaction dependent upon UDP-glucose and enzyme. The biosynthetic enzyme or enzymes displayed a relatively high degree of specificity for UDP-glucose (the best of five nucleoside diphosphate glucose substrates tried) and for the 1,2 stereoconfiguration of the diglyceride substrate. 14C-Galactose of UDP-galactose-14C is converted to glucose prior to incorporation into glycolipids of S. faecalis. Of seven 14C-diglycerides, 14C-dilinolein served best as a substrate for the synthesis of the three glucolipids. Magnesium ion stimulates the reaction. None of 18 surface active agents tried appeared to enhance the enzymatic reaction. Consistent and relatively uniform stimulation of the biosynthesis by exogenous diglyceride was best achieved by adsorbing the diglyceride substrate directly to the lyophilized enzyme preparation.