Further Studies on Extracellular Glucans Synthesized by Glucosyltransferases of Oral Streptococci

Seven water-insoluble glucans were prepared enzymatically as described previously. In addition, glucan from Streptococcus mutans strain LM7 (serotype Lancefield Group E) was 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 two methods: (1) as percent glucan solubilized based on total carbohydrate remaining in the supernatant after centrifugation, and (2) as percent reducing groups released. In all cases except glucan OMZ176, the percent carbohydrate solubilized by mutanase was greater than the percent reducing groups released. It is not necessary to hydrolyze completely a glucan in order to solubilize it. Comparison of solubilization by dextranase versus mutanase indicated that some glucans were solubilized more by dextranase, others by mutanase and some about the same. The combined hydrolytic action of the two enzymes was more effective and solubilization was more rapid than either enzyme acting separately. On some glucans their action was synergistic, the glucans were solubilized from 60 to 95%. Physical properties, such as specific rotation, intrinsic viscosity and infrared spectrum of the glucans 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 specific for α-1,3 linkage was found at 822 cm-1. Differences between glucans in susceptibility to hydrolysis, specific rotation, infrared spectra, intrinsic viscosity and reducing end groups reflect structural differences. These findings emphasize the heterogeneity of glucans that can be encountered in dental plaque.