Evidence for the presence of two distinct sites of sucrose hydrolysis and glucosyl transfer activities on 1,3-α-D-glucan synthase of Streptococcus mutans

1,3-α-D-Glucan synthase of Streptococcus mutans catalyzes both the hydrolysis of sucrose to glucose and fructose, and the glucosyl transfer to glucosyl polymers to yield water-insoluble glucan. The enzyme catalyzes only sucrose hydrolysis, however, in the absence of 1,6-α-D-glucan as an acceptor. In the present study, we found that glucosyl transfer activity was completely inhibited by the antiserum against isolated 1,3-α-D-glucan synthase but that the sucrose hydrolysis activity was not. The antiserum did not impair the binding of the enzyme to the acceptor. These findings indicate that sucrose hydrolysis and glucosyl transfer occur at two distinct sites on the enzyme.