Metabolism of the reserve polysaccharide of Streptococcus mitis. Properties of alpha-(1-->6)-glucosidase, its separation from transglucosylase, and the action of the two enzymes on branched oligosaccharides.

1. An alpha-(1-->6)-glucosidase has been separated from cell extracts of Streptococcus mitis. The enzyme was freed from transglucosylase by adsorption of the latter on retrograded amylose. 2. The enzyme was detected in five of the six strains of S. mitis that were studied; alpha-(1-->6)-glucosidase was not found in strain RB1633, a strain that did not store polysaccharide. 3. The glucosidase could act on compounds in which alpha-glucose is joined through an alpha-(1-->6)-bond to either a maltosaccharide or an isomaltosaccharide. 6(2)-alpha-Glucosylmaltose (panose) and 6(3)-alpha-glucosylmaltotriose were hydrolysed more rapidly and isomaltodextrins more slowly than isomaltose. 4. Transferring activity towards isomaltose and panose was appreciable when the concentration of substrate was 2% or higher. 5. The enzyme had no action on alpha-(1-->4)-glucosidic linkages. 6-alpha-Maltodextrinylglucoses were hydrolysed only after transglucosylase action had attenuated them to isomaltose.