Streptococcus mutans dextransucrase: availability of disaggregated enzyme after growth in a chemically defined medium

The soluble dextransucrase (EC 2.4.1.5) activity produced by Streptococcus mutans strain 6715 during growth on a chemically defined synthetic medium (FMS) was compared to enzyme from glucose broth cultures (TSB). Growth on the two media was similar. The specific activity of ammonium sulfate-precipitated FMC enzyme was 17 times greater than similar TSB enzyme preparations. The FMC enzyme was stimulated 11-fold, whereas the TSB enzyme was stimulated 1.2-fold by the addition of exogenous primer dextran. In contrast to the TSB enzyme, the FMC activity could be disaggregated to a low-molecular-weight form by 1 M salt. Thus, low-molecular-weight S. mutans dextransucrase activity free of contaminating primer glucan may be readily obtained after growth of the bacterium in a chemically defined sucrose-free medium.