In-gel SOD assay reveals SOD-2 is the single active, water-soluble SOD enzyme in C. elegans

The nematode C. elegans has a contingent of five sod genes, one of the largest among aerobic organisms. Earlier studies revealed each of the five sod genes is capable of making perfectly active SOD proteins in heterologous expression systems therefore none appears to be a pseudogene. Yet deletion of the entire contingent of sod genes fails to impose any effect on the survival of C. elegans except these animals appear more sensitive to extraneously applied oxidative stress conditions. We asked how many of the five sod genes are actually making active SOD enzymes in C. elegans through the usage of in-gel SOD activity analysis and by using KCN as a selective inhibitor against Cu-ZnSOD enzyme(s). Here we provide evidence that out of the five SOD proteins only the mitochondrial SOD is active in the water-soluble fraction of C. elegans extracts albeit at an apparently much lower activity than the multiple active SODs in D. melanogaster and E. coli. We had no opportunity to test the activity of Sod-4a isoform which is possibly a membrane-bound form of SOD. The mutant analysis further confirmed that among the two mitochondrial SOD proteins, SOD-2 is the only naturally active SOD in C. elegans.