The action of anions on catalase peroxide compounds

Abstract

The influence of pH and anions on the formation and decomposition of catalase peroxide compound n was examined. The rates of formation of compound II produced by ethyl hydroperoxide or the H2O2 generated in the notatin system, and of the decomposition induced by ethanol, show a similar proportionality to pH ([delta] log10 k = -0.6 [delta] pH). The rates of reduction of compounds I and II by the endogenous donor concerned are first-order with respect to catalase concentration; they are not signi-ficantly affected by treating the enzyme with oxidizing agents, but are modified by processes which tend to denature the enzyme protein. It is concluded that the endogenous reductions are intramolecular reactions. Anions accelerate both the reduction of compound I to II, and the reduc-tion of compound II to free catalase, in the absence of added donors. The reactions show a Michaelis -Menten relationship with respect to anion concentration, from which a Michaelis constant (Km) may be calcu-lated. For ionic ligands, Km values associated with the decomposition of compound II closely approximate the dissociation constants for the corresponding enzyme-anion complexes. For the covalent ligand cyanide, Km is much greater than the corresponding dissociation constant. Azide reacts with compound II both catalytically and stoicheiometrically as a hydrogen donor. At low hypophosphite concentrations, the rates of forma-tion of the catalase -hypophosphite complex from compound II and from free catalase are identical. The anions have no observable effect on the reduction produced by added donors. The actions of anions on catalase, peroxidase and metmyoglobin peroxide compounds are compared, and the relevance of the phenomena to the questions of the mode of action of catalase, and the nature of the endogenous donor, is discussed.