Metabolism of the reserve polysaccharide of Streptococcus mitis. Properties of glycogen synthetase

Abstract

The presence of glycogen synthetase has been demonstrated in cell extracts of five strains of S. mitis. The purified enzyme was free from transglucosylase, α-(1→6)- d-glucosidase, pullulanase, phosphorylase, and 5′-adenylate kinase, but contained a trace of branching enzyme. The enzyme transferred d-glucosyl residues from ADPG to the acceptor with the formation of α-(1 → 4)- d-glucosidic linkages. The preferred acceptors were highly branched polysaccharides. The efficiency (relative to S. mitis glycogen) of various acceptors, present in excess in activity digests, was as follows: glycogen phosphorylase limit-dextrin (107), glycogen (100), amylopectin phosphorylase limit-dextrin (78), amylopectin (65), amylopectin β-amylase limit-dextrin (30), and amylose (23). For branched oligosaccharide and polysaccharide acceptors, the side chain was the favoured site of d-glucosyl transfer. The enzyme displayed an absolute requirement for three or more d-glucosyl residues in the side chain of branched oligosaccharides of low molecular weight.