The presumed involvement of the transition metals manganese and copper in the regulation of the expression of the Mn- and CuZn-containing superoxide dismutase genes has been investigated in normal and neoplastic tissues of the rat. Two hepatomas of the Morris line have been employed, the slow growing, highly differentiated 9618A and the fast growing, poorly differentiated 3924A. The data obtained indicate a control at the pretranslational level of the Mn-containing enzyme, presumably exerted by the manganese ion. The CuZn-containing superoxide dismutase is also regulated pretranslationally in the normal tissues examined and in the hepatoma 3924A. However, there is no indication for the involvement of the copper ion, which in the liver is mostly located in the cytosol bound to CuZnSOD, in such regulation. The possible role of a reduced redox state, concomitant to the manganese deficiency in hepatoma tissues, in the down regulation of Mn-containing superoxide dismutase is discussed.
