Comparison of Cu,Zn-superoxide dismutases of clawed frogs of the genus Xenopus.

Isoenzyme profiles and thermal stability of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) of clawed frogs of genus Xenopus (X. laevis and X. borealis) were compared. Earlier the presence of an unusually thermolabile mutant Cu,Zn-SOD as well as normal enzyme was shown in X. laevis. Having confirmed the data, we further show that X. borealis contains only the thermolabile Cu,Zn-SOD. This suggested that a mutation in the Cu,Zn-SOD gene and genome duplication have occurred in the immediate predecessor of X. laevis. Later on the parent Cu,Zn-SOD gene was lost, leaving only the mutated form of Cu,Zn-SOD in X. borealis.