Purification and Characterization of Cell-associated Glucosyltransferase Synthesizing Insoluble Glucan from Streptococcus mutans Serotype c

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Abstract
Streptococcus mutans Ingbritt (serotype c) was shown to have a significant amount of cell-associated glucosyltranferase activity which synthesizes water-insoluble glucan from sucrose. The enzyme was extracted from the washed cells with SDS, renatured with Trition X-100, adsorbed to 1,3-.alpha.-D-glucan gel, and then eluted with SDS. The enzyme preparation was electrophoretically homogeneous, and the specific activity was 7.3 i.u. (mg protein)-1. the enzyme had an M1R of 158,000 as determined by SDS-PAGE, and was a strongly hdyrophilic protein, as judged by its amino acid composition. The enzyme gradually aggregated in the absence of SDS. The enzyme had an optimum pH of 6.5 and a Km value of 16.3 mM for sucrose. Activity was stimulated 1.7-fold by dextran T10, but was not stimulated by high concentrations of ammonium sulphate. Below a sodium phosphate buffer concentration of 50 mM, activity was reduced by 75%. This enzyme synthesized an insoluble D-glucan consisting of 76 mol% 1,3-.alpha.-linked glucose and 24 mol% 1,6-.alpha.-linked glucose.

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