CYTOCHEMICAL LOCALIZATION OF PEROXIDATIC ACTIVITY OF CATALASE IN RAT HEPATIC MICROBODIES (PEROXISOMES)

Abstract

Prominent staining of rat hepatic microbodies was obtained by incubating sections of aldehyde-fixed rat liver in a modified Graham and Karnovsky's medium for ultrastructural demonstration of peroxidase activity. The electron-opaque reaction product was deposited uniformly over the matrix of the microbodies. The microbodies were identified by their size, shape, presence of tubular nucleoids, and other morphologic characteristics, and by their relative numerical counts. The staining reaction was inhibited by the catalase inhibitor, aminotriazole, and by KCN, azide, high concentrations of H2O2, and by boiling of sections. These inhibition studies suggest that the peroxidatic activity of microbody catalase is responsible for the staining reaction. In the absence of exogenous H2O2 appreciable staining of microbodies was noted only after prolonged incubation. Addition of sodium pyruvate, which inhibits endogenous generation of H2O2 by tissue oxidases, or of crystalline catalase, which decomposes such tissue-generated H2O2, completely abolished microbody staining in the absence of H2O2. Neither diaminobenzidine nor the product of its oxidation had any affinity to bind nonenzymatically to microbody catalase and thus stain these organelles. The staining of microbodies was optimal at alkaline pH of 8.5. The biological significance of this alkaline pH in relation to the similar pH optima of several microbody oxidases is discussed. In addition to staining of microbodies, a heat-resistant peroxidase activity is seen in some of the peribiliary dense bodies. The relation of this reaction to the peroxidase activity of lipofuscin pigment granules is discussed.