Interspecific hybridisation in vitro of superoxide dismutase from various species

The dimeric cytosol superoxide dismutase from various organisms on different evolutionary levels has been identified and characterized by several methods: starch gel electrophoresis, inhibition by cyanide and chloroform-ethanol treatment, thermal treatment, molecular weight determined by ultracentrifugation and polyacrylamide gradient gel electrophoresis. It was found that the dimeric enzyme differs between organisms in sensitivity to thermal treatment but that the enzyme is highly resistant compared to other proteins. Most dimeric superoxide dismutase enzymes resist + 70°C for 1 hour. The enzyme from the mouse is an exception, as it resists + 100°C for 30 min without change in activity. In vitro hybridisation of chains of the dimeric enzyme from various organisms was obtained by two methods. Thermal dissociation of chains and random reassociation proved to be the best method. Hybrid molecular forms were obtained between such distantly related organisms as Neurospora crassa/Salmo salar and Ophiostoma multiannulatum/guinea. pig. It is argued that the dimeric superoxide dismutase is a conservative protein with a slow change of primary structure, which is also demonstrated by the small change in type of amino acid. The content of hydrophobic, acid and basic amino acids show the same range of change in the dimeric superoxide dismutase as in cytochrome C, which is a slowly evolving protein as judged from primary structure.