Effect of salts on water-insoluble glucan formation by glucosyltransferase of Streptococcus mutans

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Abstract
The formation of water-insoluble glucan by extracellular glucosyltransferase from S. mutans 6715 was greatly stimulated by various mono- or divalent cations. An enzyme preparation, obtained by ethanol fractionation, was able to catalyze the formation of water-insoluble glucan from sucrose in the presence of monovalent cations above 100 mM or divalent cations above 20 nM at neutral pH. As the concentration of monovalent and divalent cations was reduced to below 10 mM and 1 mM, respectively, the formation of insoluble glucan decreased to a negligible amount. High concentrations of these cations stimulated the formation of insoluble glucan in the following ways: it increased the activity of total glucosyltransferase up to 1.6- and 2.7-fold in the absence and presence of a primer dextran, respectively, and it changed the formation of soluble glucan to insoluble. It was postulated that 1 of the essential factors for the formation of insoluble glucan would be to keep more than 2 water-soluble glucan chains close to enzyme aggregates and that such interaction could be enhanced by the presence of high cation concentrations.