Streptococcus mutans strain AHT (serotype g ) secretes at least two glucosyltransferases with different PI values. A novel glucosyltransferase with a PI of 5.8 was purified 244-fold from the ammonium sulphate fraction by DEAE-cellulose chromatography, FPLC (Mono Q column, Pharmacia) and hydrophobic chromatography. The enzyme preparation gave a single protein band on analysis by both PAGE and SDS-PAGE, and did not form multiple protein bands detectable by IEF. The M , was estimated to be about 130000 by SDS-PAGE and about 135000 by ultracentrifugal analysis. The apparent K , value and pH optimum of the enzyme were 3-9 f 0.2 mM (mean ~S D ) and about 4.7, respectively. The enzyme synthesized water-soluble glucan from sucrose, and the glucan consisted of over 90 mol% 1,6-a-~-glucosidic linkages. The enzyme activity was not stimulated by primer dextran. Anti-enzyme serum produced a single precipitin band with the purified enzyme preparation, whereas it did not react with either of the other two known glucosyltransferases.
Streptococcus mutans alone or cell-free glucosyltransferase (G-Tase)-together with either Streptococcus sanguis, Streptococcus salivarius, Actinomyces viscosus, or Lactobacillus casei cells-formed artificial dental plaque that firmly adhered to glass electrodes in a continuous culture system containing sucrose. The pH in these artificial plaque samples decreased more than did that of the surrounding medium. In the absence of GTase, the bacteria other than S. mutans did not form firmly-adhering plaque on glass electrodes. The pH of the plaque formed with GTase alone did not show the pH decrease seen when the plaque contained bacteria, but, because it catalyzed the synthesis of glucan, it is suggested that the glucan acts as a diffusion barrier to retard acid loss from plaque containing acid-producing bacteria.
The water‐insolubilization mechanism of exogenous primer dextran with 1,3‐α‐d‐glucan synthase (EC 2.4.1.‐) from Streptococcus mutans was studied. The 1,3‐α‐d‐glucan synthase solution, containing sucrose and exogenous primer dextran, was incubated briefly. Water‐insoluble glucan was synthesized. At the same time, water‐soluble glucan, mainly derived from exogenous primer dextran, decreased. Linkage analysis data of glucan produced revealed that 1,3‐α‐d‐glucoside bonds increased. Exogenous primer dextran was changed by the action of 1,3‐α‐d‐glucan synthase to water‐insoluble glucan. The results suggest that in a short‐term reaction system of outside primer‐insertion type, the 1,6‐α‐d‐glucoside bond forms the main chain of water‐insoluble glucan.
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