Metabolism of the reserve polysaccharide of Streptococcus mitis. Some properties of a pullulanase

Abstract

1. A pullulanase has been separated from cell extracts of Streptococcus mitis. The enzyme was freed from transglucosylase by fractionation with ammonium sulphate. 2. Pullulanase was produced in the absence of inducers, and addition of glucose or maltose to the broth did not increase the yield of enzyme. 3. The pullulanase acted rapidly on α-(1→6)-bonds in substrates having the structure α-maltodextrinyl-(1→6)-maltodextrin, but had no action on isomaltose, 6-α-glucosylmaltodextrins or 6-α-maltodextrinylglucoses. 4. 6-α-Maltotriosylmaltodextrins were hydrolysed over 10 times faster than 6-α-maltosylmaltodextrins. 5. The branch linkages of amylopectin phosphorylase limit dextrin, glycogen phosphorylase limit dextrin and glycogen β-amylase limit dextrin were hydrolysed. The action of pullulanase on amylopectin and glycogen was accompanied by a rise in the iodine stain of 50% and 30% respectively. 6. A reversal of pullulanase action occurred on incubation with high concentrations of maltotriose. Condensation of maltosyl units to form a branched tetrasaccharide occurred less readily. 7. S. mitis pullulanase was rapidly inactivated at temperatures higher than 40°, and the enzyme did not recover activity on storage at room temperature.