Isolation and identification of a mannolipid intermediate in the synthesis of pulmonary glycoproteins

In order to demonstrate the role of lipid-linked sugars as intermediates in the synthesis of pulmonary glycoproteins, membranous preparations of rabbit lung were incubated with GDP-14C-mannose and selectively extracted with chloroform-methanol (2:1) and chloroform-methanol-water (1:1:0.3). The chloroform-methanol extract was found to contain a lipid-linked sugar which had chemical and chromatographic properties similar to mannosyl-phosphoryl dolichol. The chloroform-methanol-water extract contained an oligosaccharide-lipid and the remaining precipitate contained a labeled protein. Transfer of mannose from the labeled mannolipid to the endogenous protein was demonstrated. These studies indicate a glycolipid intermediate is present in the synthesis of oligosaccharides attached to pulmonary glycoproteins.