The Mode of Action of Plant Peroxidases

Abstract

In a recent paper' it was shown that while colloidal platinum markedly accelerates the rate of oxidation of various substances by hydrogen peroxide, it does not ordinarily bring about oxidation in the absence of hydrogen peroxide. Experiments were described, however, which show that when the colloidal metal is charged with oxygen (by making it an anode) it rapidly brings about a certain amount of oxidation. By repeating the charging process at sufficiently frequent intervals colloidal platinum might be made to bring about the oxidation of various substances at a rate approximating that affected by hydrogen peroxide and colloidal platinum. From this it was concluded that the action of the colloidal metal in accelerating oxidation by hydrogen peroxide (that is, its peroxidase action) is due to the taking of oxygen from the peroxide by the metal to form a compound which is a more efficient oxidizing agent than the original peroxide. This information, gained from a study of a simple peroxidase reaction where the constitution of the catalyzer was known, has made possible an analogous investigation of the more significant and complicated problem of the nature of the peroxidases produced in living tissue. Since, as has frequently been pointed out, the peroxidase action of colloidal platinum closely resembles that of the plant peroxidases, it seemed probable that the mechanism of the reactions must be similar. Accordingly, the experiments which proved fruitful in a study of the platinum reaction have been repeated, as nearly as the material permitted, with certain plant peroxidases. The very active ferment of horseradish root was first investigated. About I50 gm. of the finely chopped tissue was mixed with twice its volume of distilled water and allowed to stand for 24