Levels of Cu-Zn and Mn superoxide dismutases in rat liver during development

Superoxide dismutase is the main scavenger of superoxide radicals in the mammalian body. The liver has high levels of two types of superoxide dismutase enzymes, cytosolic Cu-Zn and mitochondrial Mn enzymes. The aim of the present study was to investigate the content of two distinct superoxide dismutases in liver during the perinatal transition from a hypoxic to a hyperoxic environment. Both isozymes were purified to homogeneity and used as immunogens in rabbits. Antisera raised were found to recognize only polypeptides of molecular weight 16,900 or 23,400, which correspond to Cu-Zn and Mn superoxide dismutases, respectively. It was found that the level of Cu-Zn superoxide dismutase enzymatic activity and protein as assessed by immunoquantitation increased 10-fold during the postnatal period, reaching adult levels by 3 weeks. In contrast, the amount of Mn superoxide dismutase content increased only twofold to adult levels during the first week of life. Neither of the superoxide dismutases showed an alteration in specific activity or apparent molecular weight in rat livers during ontogeny. These results show that the levels of two intracellular superoxide dismutases are differentially elevated during the perinatal period. It is suggested that each dismutase plays a different physiological role for superoxide scavenging in liver as a function of the hypoxic/hyperoxic environment at birth.