Total and insoluble dextransucrase activities were measured in cell-associated and supernatant fractions of Streptococcus mutans GS-5 grown in several media. Although the amount of cell-associated and supernatant activity varied greatly as a function of medium, the total activity appeared constant. The distribution of dextransucrase could be altered without changing the total dextransucrase activity. This indicates that the distribution of the enzyme can be regulated independently of its synthesis. Strain GS-5 had significant cell-associated activity in media devoid of sucrose. In all cases, the ratio of insoluble to total dextransucrase activity was higher in the cell-associated fractions than in the cell-free supernatants. It is also demonstrated that exogenous soluble dextran caused a decrease in insoluble dextransucrase activity and an increase in soluble dextransucrase activity in both the cell-associated fraction and the culture supernatant. The stimulation of soluble dextran-synthesizing activity was not due to de novo synthesis. The inhibition of insoluble dextran-synthesizing activity is shown to be noncompetitive. These results support a physical rather than metabolic mechanism for the effect of soluble dextran on dextransucrase activities.
