Superoxide dismutase in Didymium iridis: characterization and changes in activity during senescence and sporulation

The myxomycete Didymium iridis displays a single cytoplasmic superoxide dismutase in the diploid plasmodial stage. The enzyme was purified and appears to be a manganese-containing protein of approximately 32000 molecular weight. Superoxide dismutase specific activity was constant throughout the cell cycle and showed no significant change over the majority of plasmodial life span. Elevated superoxide dismutase activity, relative to that of other cytoplasmic enzymes, occurred during necrosis of senescent plasmodia, staling, and starvation-induced sporulation.