[Ferritin--a biocatalyst of aromatic amine oxidation].

The tetramethylbenzidine (TMB) oxidation kinetics dependent on spleen ferritin (FERR) has been studied in TMB-FERR-H2O2 (1) and TMB-FERR-O2 (2) systems at pH 4.2 and 6.0. At TMB concentrations below 6 mM, the dependencies of the initial rate for protein oxidation in system (1) on initial concentrations of TMB and H2O2 are described by the Michaelis-Menten kinetics. In terms of (kcat/K(m)), the maximum FERR efficiency during TMB oxidation is equal to 2.8-10(-1) s-1. Mannitol, urea, ethanol and sodium fluoride strongly inhibit TMB oxidation in system (1). Competitive type oxidation inhibition by urea is characterized by K(i) = 12.5 mM. At TMB concentrations above 6 mM in system (2) the autocatalytic oxidation of the amine is observed. In both systems the initial rate of TMB oxidation increases strongly with a decrease in pH from 9.3 down to 4.2. In system (1) the initiating role is played by Fe3+ ions interaction with H2O2, that in system (2)-by the interaction of the same ions with the amine proper. In both cases, TMB oxidation is a catalytic chain process including elementary ion radical stages. The main oxidizing agents in system (2) are HO radicals and Fe3+ ions. The TMB interaction with FERR may be the reason for the lipid peroxidation increase following administration of aromatic amines.