Purification and characterization of basic glucosyltransferase from Streptococcus mutans serotype c

Streptococcus mutans Ingbritt (serotype c) was found to secrete basic glucosyltranserase (sucrose: 1,6-α-^D-glucan 3-α- and 6-α- glucosyltransferase). The enzyme preparation obtained by ethanol fractionation, DEAE Bio-Gel A chromatography, chromatofocusing and preparative isoelectric focusing was composed of three isozymes with slightly different isoelectric points (pI 8.1–8.4). The molecular weight was estimated to be 151 000 by SDS-polyacrylamide gel electrophoresis. The specific activity of the enzyme was 9.8 IU per mg of protein and the optimum pH was 6.5. The enzyme was activated 2.4-fold by commercial dextran T10, and had K_m values of 7.1 μM for the dextran and 4.3 mM for sucrose. Glucan was de novo synthesized from sucrose by the enzyme and found to be 1,6- α-D-glucan with 17.7% of 1,3,6-branching structure by a gas-liquid chromatography-mass spectroscopy.