INITIATION OF RADICALS IN BIOCHEMICAL SYSTEMS - FERRITIN-HYDROPEROXIDES-AROMATIC AMINES

The rates of initiation of free radicals were determined in systems co ntaining horse spleen ferritin, H2O2, tert-butyl hydroperoxide (TBHP) or cumene hydroperoxide (CHP) in acetate buffer (pH 4.2) or phosphate buffer (pH 6.0) with 10-15% dimethylformamide (DMF). Benzidine (BD), b enzidine sulfate (BDS), o-tolidine (TL), 3,3',5,5'-tetramethylbenzidin e (TMB), and o-phenylenediamine (PDA) were used as accepters. In the s ystem ferritin-H2O2 oxidation of amine acceptor follows Michaelis-Ment en kinetics. For all aromatic amines k(cat), K-m, and their ratios wer e determined. Peroxidase efficiency of ferritin in the TMB oxidation b y hydrogen peroxide (k(cat)/K-m is characterized by a value 2.82.10(3) M-1.sec(-1) comparable with ferroxidase efficiency of apoferritin in the oxidation of Fe by oxygen. Reactivity of aromatic amines in the sy stem ferritin-H2O2 is similar to the reactivity registered in their pe roxidase oxidation and is maximal for TMB and PDA. Bimolecular rate co nstants of TMB and PDA oxidation in the reaction with H2O2, TBHP, and CHP were compared in acetate buffer (pH 4.2) using 0.5 mu M ferritin a nd 5 mM concentration of each substrate. On the oxidation of both amin es activity of oxidants decreased in the following order: H2O2 > TBHP > CHP. A scheme of radical initiation in the systems ferritin-ROOH (H2 O2)-amines and the influence of radical accepters apoferritin and orga nic co-solvent on the rate of reactions are discussed.