Further Studies on Extracellular Glucans Synthesized by Glucosyltransferases of Oral Streptococci

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Abstract
Seven water-insoluble glucans were prepared enzymatically. Glucan from Streptococcus mutans strain LM7 (serotype Lancefield Group E) was also synthesized. Glucans were hydrolyzed with dextranase mutanase and mutanase plus dextranase (1:1) until no further degradation occurred (100-150 h). Hydrolysis was measured by 2 methods: as percent glucan solubilized based on total carbohydrate remaining in the supernatant after centrifugation, and as percent reducing groups released. In all cases except glucan OMZ176, the percent carbohydrate solubilized by mutanase was greater than the precent reducing groups released. It is not necessary to completely hydrolyze a glucan in order to solubilize it. Comparison of solubilization by dextranase vs. mutanase indicated that some glucans were solubilized more by dextranase, others by mutanase and some about the same. The combined hydrolytic action of the 2 enzymes was more effective and solubilization was more rapid than either enzyme separately. The action was synergistic for some glucans solubilized 60-95%. Physical properties, i.e., specific rotation, intrinsic vicosity and IR spectrum of the gulcans was determined. A high specific rotation, low intrinsic viscosity and high ratio of free reducing end groups to total carbohydrate corresponded to a high degree of glucan branching. An absorption peak for .alpha.-1,3 linkage was found at 822 cm-1. Differences between glucans in susceptibility to hydrolysis, specific rotation, IR spectra, intrinsic viscosity and reducing end groups reflect structural differences. The heterogeneity of glucans that can be encountered in dental plaque is emphasized. The adhesion of certain oral microorganisms to smooth tooth surfaces is facilitated by cell-polymer interaction which permits clumping within a few seconds and by the agglutinating property of specific salivary glycoproteins.