Effector and precursor function of mannose 6 phosphate mannose 1 phosphate udp n acetylglucosamine and dolichylphosphate in the proteophosphomannan biosynthesis of the single cell protein yeast candida maltosa h
Roeber, B.; Reuter, G.
Journal of Basic Microbiology 25(4): 243-264
Microsomal preparations from protoplasts of the yeast C. maltosa, which is able to assimilate n-alkanes, were used as enzyme source to catalyze the incorporation of radioactivity from guanosine diphosphate 14C-mannose, 3H-mannose-6-phosphate, 3H-mannose-1-phosphate or uridine diphosphate N-acetyl-(14C-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 catalyzed the formation of an almost unsubstituted .alpha.(1,6)-linked mannan backbone from GDP-Man. Man-6P, dolichylphosphate and UDP-GNAc in the presence of ATP and dolichylphosphate are potent activators of the mannosyl transfer: .alpha.(1,2)-(and .alpha.(1,3)-) mannosyl transferases are activated by Man-6P. Man-6P is 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 mannosyl donor in the biosynthesis of proteophosphomannan.