Steryl glucoside and acyl glucoside biosynthesis in maturing pea seeds

Abstract

Sterol glucosyltransferase activity was found in a particulate fraction of pea seeds. The activity was stimulated by Ca2+ and Mg2+ and inhibited by Zn2+, Cu2+, Hg2+, EDTA and EGTA. Iodoacetamide was without effect but p-chloromercuribenzoate completely inhibited the enzyme. N -Ethylmaleimide gave 60-70 % inhibition over a wide range of concentrations. The activity was stimulated by ATP in the presence of Mg2+. Under such conditions, steryl acyl glucoside was formed. The acyl derivative was barely detectable in the presence of Ca2+ either with or without ATP. Both oleyl CoA and palmityl CoA stimulated acyl glucoside synthesis. Of the four nucleoside triphosphates, ATP, GTP, UTP and CTP both ATP and CTP stimulated acylation in the presence of Mg2+. The observations suggest that acyl donors other than digalactosyl diglyceride and phospholipids may function in steryl acyl glucoside synthesis in plants. © 1978.