Synthesis of beta-glucans in Prototheca zopfii. Isolation and characterization of the glycoprotein primer.

When Prototheca zopfii cells were pulse-labeled with 14C-containing amino acids and homogenized, 14C-labeled membranes were obtained. In vitro incubations with the previously labeled membranes and UDP-[3H]Glc produced a trichloroacetic-acid-insoluble fraction having both isotopes. A double-labeled glucoprotein was isolated and characterized. It has a relative molecular mass of 28,000-30,000 and a carbohydrate content of 10%. The oligosaccharide chain is linked to the protein through an O-glycosidic bond between hydroxyproline and glucose. The oligosaccharide has a polymerization degree ranging over 10-20 hexose units. Glucose is the only monosaccharide found; most of the glucose residues are beta-1,4-linked (90%) but some are beta-1,3-linked (10%).