Methemalbumin as biocatalyst of oxidation of aromatic amines by hydrogen peroxide

The kinetics of hydrogen peroxide-dependent oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and o-phenylenediamine (PDA) catalyzed by hemin and its complex with bovine serum albumin (BSA) was studied. Complex formation of hemin with BSA increased catalytic activity with hemin in oxidation of both amines. The reaction follows first order kinetics in concentration of biocatalyst, H2O2, and H+ in a range of pH from 6.5 to 9.0. Catalytic and Michaelis constants were calculated from double reciprocal plots of the initial rates of TMB and PDA oxidations versus their concentration catalyzed by hemin and methemalbumin. The mechanism of the radical oxidation of amines in the presence of hemin-H2O2 or hemin-BSA-H2O2 is discussed. Both systems can generate free radicals and their effectiveness is comparable to the previously studied ferritin-H2O2 system.