Glucosyltransferases of Streptococcus sobrinus C211 are both stimulated and inhibited by hydrogen peroxide

There are 2 glucosyltransferases (GTF) produced by Streptococcus sobrinus C211. One enzyme, GTF-S, produces a water-soluble glucan that is a-1,6-linked, with short a-1,3 branches, and the other enzyme, GTF-I, produces a water-insoluble glucan that is a-1,3-linked with a-1,6 branches. Hydrogen peroxide was found not only to be a potent inhibitor of GTF activity, but also a stimulator of GTF activity when employed at relatively low concentrations. At 0.88 M, H2O2 completely inhibited insoluble glucan synthesis, whereas at a 0.29 M concentration, H2O2 enhanced synthesis of the same glucan. Soluble glucan synthesis was also inhibited by H2O2 at 1.47 M. Low concentrations of hydrogen peroxide with GTF-S, however, caused the enzyme to convert from soluble glucan production to insoluble glucan production. 13C-Nuclear magnetic resonance spectra of glucans produced by peroxide-treated GTF confirmed that the production of a-1,3 linked glucans was increased with H2O2-treated GTF-S.