Oxidation of thiol compounds by catalase and peroxidase in the presence of manganese(II) and phenols [proceedings].

complex reacted rapidly with 02-. in a catalytic manner. The rate constant for O,-* dismutation was determined by competition of the iron porphyrin with Nitro Blue Tetrazolium in a xanthine/xanthine oxidase system at pH 10.1 ; a value of 3 x ~O'M-' .s-' at 20°C was obtained. The iron porphyrin had no effect on xanthine oxidase activity. Under our reaction conditions, at least 14 molecules of Oz-' reacted with each molecule of iron porphyrin. Unless catalase was added to the reaction mixture, the H2O2 generated caused degradation of the iron porphyrin to a product with a much lower Soret intensity, probably a bile-pigment type of compound. This product also catalysed dismutation of 02-' ( k = 2 X 1 o6 M-' . S-' ). In the presence of catalase, the Soret band of the iron porphyrin decreased and broadened slightly on first exposure to xanthine/xanthine oxidase, but then re-attained its original intensity. This suggests the intermediate formation of some iron(I1) porphyrin. The simplest way of representing the reaction of tetrakis-(4-N-methyl)pyridylporphine iron( 111) [Fe(III)TMpyP] with 0,-. would be: