[Methemalbumin--a biocatalyst of aromatic amine oxidation by hydrogen peroxide].

The kinetics of hydrogen peroxide-dependent oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and o-phenylenediamine catalyzed by hemin and hemin-bovine serum albumin (BSA) complex (methemalbumin) was studied in buffered physiological solution containing dimethylformamide (40%) and dimethyl sulfoxide (2%), respectively. The formation of hemin-BSA complex enhanced hemin catalytic activity in oxidation of both amines. The reaction follows first-order kinetics in biocatalyst concentrations, H2O2, and H+ ions from pH 6.5 to 9.0. The catalytic constants, Michaelis constants, and kcat/K(m) ratios for both substrates in hemin- and methemalbumin-catalyzed reactions were calculated using double reciprocal plots of the effect of the initial TMB and PDA concentrations on the initial reaction rates. Mechanism of radical oxidation of amines in hemin-H2O2 and hemin-BSA-H2O2 systems is discussed. Both systems can effectively initiate radicals free radicals formation; their activity is similar to the previously studied ferritin-H2O2 system.