Inhibition of peroxidase-catalyzed oxidations.

Chance (1) has proposed that the peroxidase-catalyzed oxidation of diiydroxyfumaric acid proceeds in two steps. The first step is the oxidation of the hydrogen donor by oxygen, the reaction being catalyzed by a manganese-activated peroxidase and accompanied by the production of hydrogen peroxide. The second step is the oxidation of additional hydrogen donor by hydrogen peroxide, this reaction again being catalyzed by peroxidase. Akazawa and Corm (2) have proposed an analogous mechanism for the peroxidase-catalyzed oxidation of reduced diphosphopyridine nucleotide. An alternative mechanism for peroxidasecatalyzed oxidations was suggested by Kenten and Mann (3) who observed that manganese was oxidized during the peroxidase-catalyzed oxidations of organic acids. They considered that the manganese was oxidized enzymically, and that the manganic ions formed were necessary for the oxidation of the hydrogen donors. This function of manganese has been incorporated into the mechanism of oxidation of indoleacetic acid presented by Maclachlan and Waygood (4). Inhibitors have been employed in the present study to obtain more information on the mechanism of peroxidase-catalyzed oxidations. The data show the similarity of DPNH and indoleacetic acid oxidation and suggest that peroxidase-catalyzed oxidations may proceed by diierent mechanisms at different concentrations of manganese.