INACTIVATION OF AN ANIMAL AND A FUNGAL CATALASE BY HYDROGEN-PEROXIDE

We have quantitatively compared the rates of peroxide-dependent inacti vation of bovine liver catalase and Aspergillus niger catalase as clas s representatives of catalases that contain tightly bound NADPH and th ose that do not. Inactivation of these catalases in the presence of et hanol has also been quantitated in an effort to assess the importance of compound II, an inactive form of bovine liver catalase, in the inac tivation reaction. The values of K-2, the second-order rate constant f or inactivation calculated for the bovine enzyme, in the absence and p resence of ethanol, respectively, were 8.9 +/- 0.26 and 8.5 +/- 0.27 M (-1) min(-1). In contrast, the values for the A. niger enzyme were 0.5 1 +/- 0.069 and 10.5 +/- 0.32 M(-1) min(-1). The A. niger enzyme is mo re stable toward hydrogen peroxide-induced inactivation than the liver enzyme. The A niger enzyme is markedly destabilized by 20 mM ethanol, whereas the inactivation of the liver enzyme is unaffected by ethanol . Reaction of bovine liver catalase with ethyl hydroperoxide produced the characteristic absorption spectrum of compound I and in the absenc e of ethanol the spectrum associated with compound II. In contrast, th e fungal enzyme developed compound I spectrum but spectral changes tha t might be ascribed to compound II were barely detected in the Soret r egion. Spectral changes for A. niger catalase in the visible region we re modified by the presence of ethanol but could not be clearly correl ated with the bovine catalase compound II spectra either in the presen ce or absence of ethanol. The stability of the fungal and bovine catal ases in the presence of hydrogen peroxide is quantitatively documented . The enzymes are also shown to be different in their response to etha nol and in the formation of compound II-like species with ethyl hydrop eroxide. It appears unlikely that compound II is an intermediate in th e hydrogen peroxide-mediated inactivation reaction of either catalase under catalatic assay conditions. (C) 1995 academic Press,Inc.