The Biosynthesis of Mannan in Saccharomyces carlsbergensis

A particulate preparation obtained by lysing yeast protoplasts was found to catalyze the incorporation of radioactivity from guanosine diphosphate 14C-mannose into a mannose polysaccharide. The km for guanosine diphosphate mannose is 0.5 mm, and the optimum pH is between 5.5 and 7.2. There is an almost absolute requirement of Mn++ for activity, which cannot be substituted by Mg++. The reaction proceeds in the absence of added primer. The reaction product was identified as yeast mannan by comparing the oligosaccharides prepared by acetolysis with those from a radioactive mannan obtained in vivo. The results of the reduction and hydrolysis of these oligosaccharides are consistent with the assumption that a representative part of the mannan molecule is synthesized by the preparation. The reaction product remains attached to particles, from which it can be partially released by mild treatments, such as incubation at 37° or heating at 100° at pH 7.5. Several enzymes also release the radioactivity from the particles. The possible significance of these findings in relation to the passage of mannosyl residues from the inside to the outside of the cytoplasmic membrane and their integration into the cell wall is discussed.