Role of superoxide dismutase in a copper-resistant strain of yeast

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A copper-resistant yeast strain (R_<Cu>) which was cultured repeatedly in a medium containing 1 mM Cu was found to contain a large amount of superoxide dismutase. When yeast cells, which had been grown under different conditions and accordingly had various levels of superoxide dismutase activity, were exposed to copper under nongrowing conditions and plated onto normal medium, the more dismutase they had, the higher was their survival ratio. When the cells were exposed to cadmium instead of copper, the survival ratios were independent of their enzyme activity. The results suggest that the toxicity of a transition metal such as copper is necessary to account for the toxicity of superoxide radicals produced by reactions of copper and thiols in the cell components. On the other hand, when the same yeast cells were plated directly onto copper-containing medium, only R_<Cu> showed a marked high survival ratio. Hence, it is concluded that the cells need to overcome the toxicity of superoxide radicals to grow in the copper-containing medium, but a more effective resistant mechanism(s) must be present in R_<Cu> cells. The role of superoxide dismutase induced in R_<Cu> is discussed.
日本植物生理学会の論文