Immunogenic properties of the glucosyltransferase from Streptococcus sanguis OMZ 9: kinetic study of inhibition by antibodies.

An anti-glucosyltransferase serum was prepared against a pure enzyme preparation from Streptococcus sanguis OMZ 9, which synthesized both soluble and insoluble dextran. Sera, crude gamma globulins, and antibody fractions obtained after gel filtration on a Bio-Gel P200 column were used to study enzyme-antibody interactions. A strong inhibition of glucosyltransferase activity was obtained only with the purified antibody fraction. Kinetics studies showed that the anti-glucosyltransferase antibodies acted as noncompetitive inhibitors with respect to the substrate (sucrose). The addition of primer dextran in the reaction mixture during preincubation produced a diminution of the inhibition, and the antibodies acted as mixed type inhibitors with respect to dextran. The simultaneous addition of dextran and antibodies can protect the enxyme against antibody inhibition.