Formation of polyprenol-linked mono- and oligosaccharides in Phaseolus aureus

Abstract

A crude membrane preparation from Phaseolus aureus hypocotyls catalyzes the incorporation of mannose from GDP-[ 14C]mannose into a acid labile glycolipid and a methanol insoluble fraction. Addition of dolichyl monophosphate to the incubation mixture stimulated the formation of both the mannolipid and the methanol insoluble endproduct. Thin-layer chromatography of endogenous lipid and of the stimulated lipid fraction revealed that both compounds run identical. Ficaprenyl monophosphate also stimulates the incorporation of mannose; however, the ficaprenyl monophosphate mannose formed is not identical to the endogenous mannolipid. This suggests that the endogenous acceptor has the properties of an α-saturated polyprenyl monophosphate rather than those of the ficaprenyl phosphate type. The same membrane preparation also incorporates N-acetylglucosamine into an acid labile glyolipid as well as into a polymer fraction. Evidence is presented that the N-acetylglucosamine containing lipid consists of a mixture of dolichyl pyrophosphate N-acetylglucosamine and dolichyl pyrophosphate di- N-acetylchitobiose. It seems likely that the two compounds have a precursor-product relationship. Incubation of dolichyl pyrophosphate di- N-acetylchitobiose together with GDP-mannose gives rise to lipid-bound mannosyl-di- N-acetylchitobiose. Radioactivity from either the [ 14C]mannolipid or the N-acetyl[ 14C]glucosamine containing lipid is incorporated into a methanol insoluble product to 3.4 and 6.3%, respectively; it seems, at least in part, to be a glycoprotein.