Metabolism of the Reserve Polysaccharide of <i>Streptococcus mitis</i>

Abstract

The properties of a purified branching enzyme (α‐1,4‐glucan : α‐1,4‐glucan 6‐glycosyltransferase) isolated from intracellular extracts of several strains of Streptoccus mitis were studied with maltodextrins, amylose, amylopectin and glycogen as substrates. Maltodextrins with an average degree of polymerization above 20 were good substrates, and the rate of branching enzyme action increased with chain‐length. The enzyme had a higher affinity towards branched substrates than linear polysaccharides, and evidence of its ability to convert glycogen into a more highly branched product is presented. The rate of synthesis of glycogen by glycogen synthetase was increased when branching enzyme was present. The activating and protective effect of citrate ions on branching enzyme is described, and the way in which citrate could regulate the degree of branching that occurs during glycogen synthesis is discussed.