ULTRACYTOCHEMICAL LOCALIZATION OF SUPEROXIDE DISMUTASE ACTIVITY IN RABBIT ALVEOLAR MACROPHAGES : A COMPARATIVE STUDY USING KO_2 OR XANTHINE-XANTHINE OXIDASE AS O-_2 GENERATING SYSTEM

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An attempt has been made to obtain evidence for the localization of superoxide dismutase (SOD) activity in rabbit alveolar macrophages (AMφ). SOD localization was investigated with two different superoxide (O-_2)-generating systems, the potassium superoxide (KO_2) and the xanthine-xanthine oxidase system. The hydrogen peroxide (H_2O_2) generation site, which indicates SOD activity, was electron cytochemically investigated by using the cerium method introduced by Briggs et al. In the KO_2 system, the formation of cerium perhydroxide serves as an indication of SOD activity, and its presence was confirmed throughout the cytoplasm and mitochondria, but not in the nucleus and granules. Under the action of diethyldithiocarbamate and potassium cyanide, which act as Cu, Zn-SOD inhibitors, it was found that the cytoplasmic SOD activity was virtually completely suppressed, and that complete inhibition of SOD activity occurred in the presence of catalase (a scavenger of H_2O_2) or in the absence of KO_2. In the xanthine-xanthine oxidase system, cerium deposits were observed in the cytoplasm, but rarely in the mitochondria. Occasionally some reaction product was seen in the nucleus and granules. From the results, it is concluded that KO_2 system is an excellent method for investigation of the localization of SOD activity.
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