Isolation and some properties of extracellular d-glucosyltransferases and d-fructosyltransferases from Streptococcus mutans serotypes c, e, and f

Abstract

Extracellular d-glucosyltransferases (GTase) and d-fructosyltransferases (FTase) were isolated from Streptococcus mutans IB (serotype c), B14 ( e), and OMZ175 ( f) by chromatofocusing, followed by hydroxyapatite column chromatography. The GTases isolated from serotypes c, e, and f are basic proteins (pI 7.4). The serotype c and e enzymes have two protein components having M r 173 000 and 158 000 and the enzyme of the serotype f one component having M r 156 000. The GTases of all the serotypes showed a K m value for sucrose of 10–14m m and an optimum pH 5.5–6.0 for enzyme activity, and their activities were enhanced by the presence of primer Dextran T10. The α- d-glucans synthesized by the purified GTases are water soluble and primarily consist of (1→6)-α- d-glucosidic linkage (41–66 mol/100 mol) and α- d-(1→3,6)-branch linkage (6–20 mol/100 mol), but significant proportions of α- d-(1→3), α- d-(1→4), and α- d-(1→3,4) linkages (11, 6, and 14 mol/100 mol, respectively) were detected in the serotype c α- d-glucan. The isolated FTases of the serotypes c, e, and f are acidic enzymes (pI 4.6) and consist of two components having M r 84 000 and 76 000 for the serotype c enzyme, and 106 000 and 84 000 for the serotypes e and f enzymes, respectively. The K m value for sucrose was 6, 10, and 17m m for the serotypes c, e, and f enzymes, respectively, and the optimum pH of enzymic activity 5.5–6.0. Reactivity with Concanavalin A, susceptibility to acid hydrolysis, and paper chromatography of the hydrolyzates suggested that the water-soluble β- d-fructans synthesized by the purified FTases were of the inulin-type and had chemical structures somewhat different among the serotypes.