Heterogeneity of copper-induced superoxide dismutase in rat liver lysosomes

Preparations of liver large granule fraction from control and copper-injected rats were treated with digitonin (0.01-0.16 mg/mg protein) and supernatants rich in lysosomal matrix and in mitochondrial intermembrane space were obtained. After copper injection the superoxide dismutase activity in all supernatants was significantly increased. The granular CuZn-superoxide dismutase in the two animal groups was localized in lysosomes only. The cytosolic and lysosomal CuZn-superoxide dismutase in control preparations showed an equal electrophoretic pattern (two peaks with Rf = 0.42 and 0.47). After copper injection three new electrophoretic peaks of the lysosomal CuZn-superoxide dismutase activity (with Rf = 0.37, 0.52 and 0.62 respectively) appeared. The increased heterogeneity of the granular CuZn-superoxide dismutase activity after copper injection is explained by the oxidative degradation of the CuZn-superoxide dismutase in lysosomes.