We have shown in previous studies that the glucosyltransferase (Gtf) enzymes of Streptococcus mutans have distinct properties when adsorbed to a surface. In the present study, we compared the activity of Gtf from Streptococcus sanguis, designated GtfSs, in solution and on the surface of saliva–coated hydroxyapatite (sHA) beads, and determined the ability of its product glucan to support the adherence of oral microorganisms. Gtf from S. sanguis 804 NCTC 10904 was purified from culture supernatant fluids by means of hydroxyapatite chromatography. Enzyme and the substrate were prepared in buffers at pH values from 3.5 to 7.5. Maximum activity of GtfSs occurred between pH 5.5 and pH 6.5, whether in solution or adsorbed onto a surface. The solubilized and insolubilized enzymes showed highest activity at 40°C; activity was reduced by 50(±2)% at 20 and 30°C. The enzyme did not form glucans in either phase at 10 or 60°C. The Km, determined from Lineweaver–Burk plots, for the enzyme in solution was 4.3(±0.4) mmol/l sucrose, and the Km for the enzyme on sHA beads was 5.0(±1.0) mmol/l sucrose. The ability of the GtfSs glucan synthesized on the surface of sHA beads to support the adherence of oral bacteria was investigated. 3H–thymidine–labeled bacteria (S. mutans GS–5, S. sobrinus 6715, S. sobrinus 6716, S. sanguis 10904, Actinomyces viscosus OMZ105E, A. viscosus 2085, and A. viscosus 2086) were incubated with sHA beads coated with GtfSs glucan. S. mutans GS–5 displayed the highest level of binding numerically. These results show that the GtfSs of S. sanguis is active on sHA beads, that the pH optimum for activity on a surface differs slightly from that in solution, and that its product glucan can support the adherence of oral microorganisms.

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