Biosynthesis of Dolichol Derivatives Containing D-Galactose in Calf Pancreas Microsomes

Abstract

This chapter describes the biosynthesis of dolichol derivatives containing D-Galactose in calf pancreas microsomes. Calf pancreas microsomes synthesize dolichol derivatives of acetyl glucosamine, mannose, and glucose. These compounds are intermediates in the biosynthesis of the inner-core region of asparagines-linked oligosaccharides in glycoproteins. However, why certain glycosyltransferase reactions require the participation of dolichol derivatives is not known. When calf pancreas microsomes were incubated with UDP-D-[ 14 C] galactose, radioactivity was incorporated for about 20 min into lipid fractions extracted with chloroform–methanol (2:1) (CM extract) and chloroform–methanol–water (10:10:2.5) (CMW extract) and into the residual precipitate (Ppt) containing glycoproteins. The chromatographic behavior of the galactose-containing lipid in DEAE-cellulose and of the oligosaccharide derived from it by mild acid treatment is similar to that of the dolichyl pyrophosphate oligosaccharides previously isolated from calf pancreas microsomes. Although the role of these compounds in the biosynthesis of complex carbohydrates remains to be elucidated, it is possible that the dolichyl pyrophosphate oligosaccharides containing galactose are concerned with the biosynthesis of glycoproteins with unusual carbohydrate composition—consisting of mannose, N-acetylglucosamine, glucose, and galactose—found in certain lysosomal enzymes and in mesenchymal tissues.