Superoxide dismutase: tissue, cellular, and subcellular distribution in adult canine heart

Cell-free extracts of canine myocardial tissue were found to contain two biochemically and electrophoretically distinct superoxide dismutases (SOD), an enzyme that provides defense against the deleterious effect of superoxide radicals (O2.-). Polyacrylamide gel (7.5%) electrophoresis revealed two distinct bands of SOD activity: a slower moving band [retardation factor (Rf) = 0.4] resembling the manganese SOD found in bacteria and mitochondria (which is not inhibited by 2.5 mM cyanide) and a faster moving band (Rf = 0.75) that is sensitive to cyanide. In contrast, extracts from isolated adult canine cardiac myocytes were found to contain only the cyanide-insensitive SOD. Extracts of whole myocardium and isolated cardiac myocytes contain 22.3 +/- 1.2 and 27.0 +/- 1.5 U cyanide-insensitive SOD/mg protein, respectively. However, the activity of cyanide-sensitive SOD in these fractions is 7.9 +/- 2.0 (tissue) and 1.5 +/- 1.4 (cells) U/mg protein. Cardiac myocyte SOD activity was particulate in nature, and the major part of the SOD activity was associated with heavy mitochondrial fractions. The biologic significance of this higher activity of SOD in the heavier mitochondrial fraction remains to be elucidated.