Purification and Characterization of Extracellular Glucosyltransferase from Streptococcus mutans Serotype b (Subspecies rattus)

Summary: An extracellular glucosyltransferase (GT-S) synthesizing water-soluble glucan was purified from the culture supernatant of Streptococcus mutans BHT (serotype b, subsp. rattus) by DEAE-Sepharose chromatography and preparative isoelectric focusing. The M r of the enzyme was 155000 and the pI was 4·5. The GT-S had a specific activity of 10·2 i.u. (mg protein)−1, an optimum pH of 6·0 and a Km value of 0·8 mm for sucrose, and was activated twofold by dextran T10. The GT-S was immunologically partially identical with the corresponding enzymes in crude preparations from serotypes c, e and f. The glucan synthesized de novo from sucrose by the GT-S was water-soluble and consisted of 29 mol% of non-reducing terminal, 49 mol% of 1,6-α-linked, 11 mol% of 1,3-α-linked and 11 mol% of 1,3,6-α-branched glucose residues.