Abstract
Cell-free d-glucosyltransferase of d-glucose-grown Streptococcus mutans AHT was completely inactivated in the presence of 0.002% of Methylene Blue at 25° and pH 7.0 after illumination with a 150-W incandescent lamp. The rate of inactivation was decreased at pH values <7.0. Histidine was the only amino acid residue modified to a significant extent, and the rates of oxidation of histidine residues and loss of enzyme activity closely agreed. Production of both water-insoluble and -soluble d-glucan fractions from sucrose by the oxidized d-glucosyltransferase preparations was significantly inhibited. Photooxidation with 0.002% of Rose Bengal at pH 7.0 or higher also induced complete inactivation of the d-glucosyltransferase. These results strongly suggest that the imidazole portion of histidine may function as part of the active sites of both d-glucosyltransferase isozymes of S. mutans AHT, which are responsible for the synthesis of (1→3)- and (1→6)-α- d-glucosidic linkages. The d-glucosyltransferases from S. mutans 6715 and AHT-mutant Ml, and Streptococcus sanguis ATCC 10558 were also almost completely inactivated by Methylene Blue-sensitized photooxidation.
Published Version
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