Biosynthesis of Monogalactosyl Diglycerides in Photoauxotrophic Euglena gracilis

Abstract

Abstract Cell-free extracts of green Euglena gracilis catalyze the transfer of stearoyl and oleoyl groups from thioesters of Escherichia coli acyl carrier protein to monogalactosyl diglycerides. This reaction was stimulated by α-glycerophosphate. In the course of the transfer reaction, stearic acid was partly desaturated to unsaturated acids. Palmitoyl acyl carrier protein was poorly utilized in galactolipid synthesis. In the same system monogalactosyl diglycerides accepted acyl groups also from oleoyl-CoA. In none of the experiments did the digalactosyl diglycerides become labeled significantly. The fatty acyl carrier protein thioesters did not serve as substrate for phospholipid synthesis. Acyl groups from CoA thioesters were, however, transferred to the phospholipids. This reaction was not stimulated by added α-glycerophosphate and may not represent synthesis de novo. Waxlike lipids incorporated appreciable amounts of radioactivity from 1-14C-acyl-CoA derivatives.