Characterization of extracellular glucosyltransferase activity of Steptococcus mutans

The extracellular glycosyltransferase activity of Sterptococcus mutans GS-5 has been resolved into two non-overlapping fractions after gel filtration chromatography on Bio Gel A-15 columns. The activity eluting in the void volume, fraction A, was highly aggregated and synthesized both soluble and insoluble glucans. The activity retarded by the resin, fraction B, synthesized only soluble glucan. Almost all of the extracellular glucosyltransferase activity was eluted in the void volume when the cells were grown in Todd-Hewitt medium. However, most of the activity migrated as the lower-molecular-weight species when cells were grown under conditions which inhibit insoluble glucan formation. The activities in both fractions had identical temperature and pH optima as well as similar Km values for sucrose. Fraction A synthesized both alpha-1,3- and alpha-1,6- linked glucans, whereas fraction B catalyzed alpha-1,6-glucan formation. Fraction B has been purified to near homogeneity and is also aggregated with a subunit molecular weight of 45,000. The properties of the glucosyltransferases in both fractions are discussed in terms of the role of the enzymes in both soluble and insoluble glucan formation.