Studies on saccharogenic amylase from Rhizopus javanicus. IV. The structure of the carbohydrate moiety of a glycopeptide GP-I-b from Rhizopus saccharogenic amylase.

Abstract

The structure of the carbohydrate moiety of GP-I-b which is one out of three glycopeptides isolated from a Pronase digest of the saccharogenic amylase of Rhizopus javanicus sp. 3-46, was investigated by enzymatic and chemical techniques. Nine moles of mannose followed by one mole of N-acetylglucosamine were released per mole of GP-I-b when it was treated sequentially with purified jack bean α-mannosidase and β-N-acetylglucosaminidase. Methylation of GP-I-b gave 3, 6-di-O-methyl derivative from the N-acetylglucosamine residues, and 2, 3, 4, 6-tetra-O-methyl, 3, 4, 6-tri-O-methyl and 2, 4-di-O-methyl derivatives from the mannose residues in an approximate ratio of 3:4:2. A smaller glycopeptide (F-1) containing two moles each of mannose and N-acetylgluco-samine per mole of asparagine was obtained when GP-I-b was subjected to one step of the Smith degradation. Exhaustive methylation of F-1 gave 3, 6-di-O-methyl derivative of N-acetylglucosamine, and 2, 3, 4, 6-tetra-O-methyl and 2, 3, 4-tri-O-methyl derivatives of mannose in a ratio of 1.00:0.85. Controlled acetolysis of GP-I-b yielded mannose, O-α-mannosyl-(1→2)-O-α-mannosyl-(1→3)-mannose and a smaller glycopeptide which was resistant to the acetolysis. From these and previous evidences, the following structure was determined for GP-I-b.