Superoxide dismutase of Cryptococcus neoformans: purification and characterization.

We have purified to homogeneity a putative superoxide dismutase of 19.5 kDa from the pathogenic yeast Cryptococcus neoformans by homogenization, isoelectric focusing and gel filtration. The N-terminal amino acid sequence of this protein indicates a significant sequence homology with known manganese-containing superoxide dismutases (Mn-SODs) from various organisms. In addition, the presence of superoxide dismutase activity was confirmed using specific substrate gels which detect this enzyme when nitro-tetrazolium blue reduction is prevented by the photochemical source of superoxide, in the presence of riboflavin when exposed to light. Superoxide dismutase activity was also assayed using cytochrome c. The molecular weight of the native enzyme (on non-denaturing gels) is 80 kDa. The optimum pH for the enzyme is 7.5 and its pi = 6.6. The enzyme was inhibited by sodium dodecyl sulphate, sodium azide, o-phenanthroline, and EDTA, in descending order.