title: Reduction of lactoperoxidase by the dithionite anion monomer.
abstract: The reduction of lactoperoxidase with sodium dithionite has been studied by means of stopped-flow spectrophotometry in an anaerobic system. Under pseudo-first-order conditions the rate constant was found to be linearly dependent on the square root of the dithionite concentration, which confirms the monomeric radical, SO2- as the reducing species. The second-order rate constant is moderately influenced by increased ionic strength but drastically increased at lower pH. The pH dependence supports the previously suggested existence of a carboxyl group, essential to the different enzymatic functions of lactoperoxidase. The second-order rate constant for the reduction of lactoperoxidase at pH 7.0 (kappa 1 = 1.3 X 10(5) M-1 s-1) was about three times higher than the rate constant for the reduction of cyanide-bound lactoperoxidase and two times the rate constant for the reduction of the fluoride-lactoperoxidase complex.
mesh_terms: D004227:Dithionite / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007784:Lactoperoxidase; D010084:Oxidation-Reduction; D010544:Peroxidases; D012044:Regression Analysis; D013447:Sulfites / Q000494:pharmacology*
chemical_list: D013447:Sulfites; D004227:Dithionite; D007784:Lactoperoxidase; D010544:Peroxidases