Participation of metals in peroxidasecatalyzed oxidations.

The requirement for manganese in peroxidase-catalyzed oxidations has hitherto been considered to be very specific. Various investigators (l-6) have tested a number of other ions (Zn, Mg, Cu, Co, Fe, Ni, Cd, Ca, Al, Sn, and molybdate) in different peroxidase-catalyzed oxidations, but with the exception of a slight stimulation of reduced diphosphopyridine nucleotide oxidation by cobaltous ions, these ions have proved inactive or inhibitory. In view of the suggestions that the peroxidase-catalyzed oxidations of dicarboxylic acids (7) and the peroxidase-catalyzed oxidation of indoleacetic acid (8) depend on the formation of manganic ions, it is interesting that the peroxidase system of Kenten and Mann (9) oxidized manganese only. Ions of copper, cobalt, zinc, nickel, and iron were not affected. However, Yamada and Ota (10) have reported the oxidation of ferrous ions by a preparation from rice roots; they considered the responsible enzyme to be a peroxidase. The possibility that cerium might be oxidized by a peroxidase system and might replace manganese in peroxidase-catalyzed oxidations was considered because of the closeness of the oxidation-reduction potential of cerium to that of manganese, and because of the known initiation of oxidations by ceric ions (11). It has been found that cerous ions will replace manganous ions in the three peroxidase-catalyzed oxidations examined.