Dolichol Pathway in Lymphocytes from Rat Spleen

Abstract

Incubation of rat spleen lymphocytes with UDP-glucose together with GDP-mannose and UDP-N-acetylglucosamine leads to the formation of glucosylated lipid intermediates characterized as dolichyl phosphate glucose and dolichyl diphosphate oligosaccharides. This latter can be either transferred onto endogenous protein acceptors or cleaved into phosphooligosaccharides. The striking fact is that phosphooligosaccharide populations contain far less glucosylated products than the dolichyl diphosphate oligosaccharide ones from which they are derived. Two hypotheses were investigated: either a rapid action of glucosidases on the liberated phosphooligosaccharides or a preferential splitting of the non-glucosylated population of dolichyl diphosphate oligosaccharides. Addition of p-nitrophenyl-.alpha.-D-glucoside inhibits glucosidase activities and allows the production of a major population of dolichyl diphosphate oligosaccharides containing 3 glucose residues. Using these conditions, the amount of phosphooligosaccharides generated from the splitting of dolichyl diphosphate oligosaccharides is greatly decreased and that the major part of these remaining phosphooligosaccharides do not contain glucose. The presence of glucosyl units prevent dolichyl diphosphate oligosaccharides from further degradation into phosphooligosaccharides.