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
Mr 173 000 and 158 000 and the enzyme of the serotype
f one component having
Mr 156 000. The GTases of all the serotypes showed a
Km value for sucrose of 10–14mm 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
Mr 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
Km value for sucrose was 6, 10, and 17mm 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.
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