Characterization of cell-associated dextransucrase activity from glucose-grown cells of Streptococcus mutans.

Two distinct forms of cell-associated dextransucrase activity have been extracted from glucose-grown cells of Streptococcus mutans GS-5. One form can be washed from cells by treatment with hypertonic salt solutions. This activity is located on the exterior of the cell since it is susceptible to inactivation by proteolytic enzymes. Gel filtration of the extracted enzyme indicates that the enzyme exists as a highly aggregated complex which dissociates into a smaller soluble species in the presence of hypertonic salt solutions. This form of the enzyme also plays a role in sucrose-dependent adherence of whole cells to smooth surfaces. Hypertonic salt solutions also elute most of the cell-associated dextransucrase activity from strain FA-1 but not from strain HS-6. The second cell-associated activity of strain GS-5 is released after disruption of washed cells, is not susceptible to proteolytic enzyme treatment of whole cells, and represents the intracellular form of the enzyme. A comparison of the gel filtration properties. pH and temperature optima, kinetic constants, and insoluble dextran-synthesizing activities of the two cell-associated forms of the enzyme with the extracellular enzyme did not reveal any major differences.