PURIFICATION AND CHARACTERIZATION OF AG,ZN-SUPEROXIDE DISMUTASE FROM SACCHAROMYCES-CEREVISIAE EXPOSED TO SILVER

Cu,Zn-superoxide dismutase plays an important role in protecting cells from oxygen toxicity by catalyzing the dismutation of superoxide anio n into hydrogen peroxide and oxygen. In Saccharomyces cerevisiae Cu,Zn -superoxide dismutase is coregulated with copper-thionein by copper vi a the transcription factor ACE 1. We demonstrate here that presence of AgNO(3) in the culture medium leads to a five times increase of Cu,Zn- superoxide dismutase mRNA, with a concomitant six times decrease of th e enzyme activity. Susceptibility of yeast to silver was apparently in versely related to Cu,Zn-superoxide dismutase activity. From silver-tr eated yeast a Cu,Zn-superoxide dismutase with impaired dismutase funct ion was purified and was shown to contain silver, which was located to the copper site. These data suggest that Cu,Zn-superoxide dismutase m ay play an additional direct role in the defense of S. cerevisiae agai nst metal stress by functioning as metal chelator.