Inactivation of D-glucosyltransferases from oral Streptococcus mutans and Streptococcus sanguis by photochemical oxidation.
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 degrees and pH 7.0 after illumination with a 150-W incandescent lamp. The rate of inactivation was decreased at pH values less than 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 goes to 3)- and (1 goes to 6)-alpha-D-glucosidic linkages. The D-glucosyltransferases from S. mutans 6715 and AHT-mutant M1, and Streptococcus sanguis ATCC 10558 were also almost completely inactivated by Methylene Blue-sensitized photooxidation.
D000596:Amino Acids / Q000032:analysis; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009055:Mouth / Q000382:microbiology; D010084:Oxidation-Reduction; D010782:Photolysis; D013045:Species Specificity; D013291:Streptococcus / Q000201:enzymology*
D000596:Amino Acids; D005964:Glucosyltransferases