Effektor‐ und Precursorfunktion von Mannose‐6‐phosphat, Mannose‐l‐phosphat, UDP‐N‐acetylglucosamin und Dolichylphosphat bei der mikrosomalen Biosynthese von Proteophosphomannan der SCP‐Hefe Candida maltosa H

Microsomal preparations from protoplasts of the yeast Candida maltosa , which is able to assimilate n ‐alkanes, were used as enzyme source to catalyse the nicorporation of radioactivity from guanosine diphosphate 14 C‐mannose, 3 H‐mannose‐6‐phosphate, 3 H‐mannose‐1‐phosphate or uridine diphosphate N‐acetyl‐( 14 C‐glucose)‐glusosamine in a mannose polysaccharide. The reaction product was identified as yeast mannan by comparing the saccharides prepared by alkaline degradation and by acetolysis, with those from in vivo proteophosphomannan, obtained in structural investigations. The enzyme preparation catalysed the formation of an almost unsubstituted α(1,6)‐linked mannan backbone from GDP‐Man. Man‐6P, dolichylphosphate and on the other hand UDP‐GNAc in the presence of ATP and dolichylphosphate are potent activators of the mannosyl transfer: α(1,3)‐(and α(1,3)‐) mannosyl transferases are activated by Man‐6P. Beside this Man‐6P is found to be a precursor for the incorporation of the first mannosyl (‐phosphate) unit in the side chain of a branched mannan and of the alkali‐labile bound oligosaccharides. The data presented support the hypothesis that Man‐6P, not activated by GTP, is a second mannosyldonator in the biosynthesis of proteophosphomannan.