Studies on Phyto-peroxidase

Part XXI. High-spin Form of Japanese-radish Peroxidase c

Abstract

Japanese-radish peroxidase c, a paraperoxidase exhibiting the optical absorption spectrum of low-spin nature, was found to transform to a high-spin state by removing a dissociable ligand of low molecular weight by the addition of the stoichiometric amount of p-chloromercuribenzoate, as in the case of horseradish peroxidase I or wheat germ peroxidase 566. The reaction could be reversed by the addition of cysteine to remove p-chloromercuribenzoate. As this ligand would be possibly cyanide, the affinity of the high-spin form of the enzyme to sodium cyanide was determined, which was found to be much higher than that of Japanese-radish peroxidase a. The high-spin form of peroxidase c formed the usual Compound I by the addition of hydrogen peroxide, so that the peroxidatic reaction catalyzed by this enzyme should follow the common mechanism of plant peroxidases. However, Compound II was scarecely observed during the course of the stepwise reduction of Compound I by ascorbate, probably because of its more rapid conversion to the free enzyme.