The localization of catalase in the pulmonary alveolar macrophage

A combined biochemical and cytochemical study of catalase was performed on alveolar macrophages lavaged from the lungs of adult male rats. Biochemically, catalase activity was present in both a high-speed granule fraction and in the supernatant. The granule-associated activity exhibited latency. Two methods of cell breakage, sonication and homogenization, yielded similar levels and distributions of catalase activity. Catalase activity in whole cells was identified cytochemically by the alkaline diaminobenzidine method and was localized within membrane-lined cytoplasmic granules similar in size to microperoxisomes and associated with cisternae of smooth endoplasmic reticulum. Localization of the reaction product was inhibited by 0.04 M aminotriazole, by cyanide, and by boiling prior to incubation. The cytochemical reaction continued in the absence of exogenous peroxide, but could be prevented by addition of catalase or pyruvate to the peroxide-free medium. Enzyme activity was also localized within a portion of the membrane-bound granules present in the cell fractions used for the biochemical assays.