Tamai K T, Gralla E B, Ellerby L M, Valentine J S, Thiele D J
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor 48109-0606.
Proc Natl Acad Sci U S A. 1993 Sep 1;90(17):8013-7. doi: 10.1073/pnas.90.17.8013.
Copper-zinc superoxide dismutase catalyzes the disproportionation of superoxide anion to hydrogen peroxide and dioxygen and is thought to play an important role in protecting cells from oxygen toxicity. Saccharomyces cerevisiae strains lacking copper-zinc superoxide dismutase, which is encoded by the SOD1 gene, are sensitive to oxidative stress and exhibit a variety of growth defects including hypersensitivity to dioxygen and to superoxide-generating drugs such as paraquat. We have found that in addition to these known phenotypes, SOD1-deletion strains fail to grow on agar containing the respiratory carbon source lactate. We demonstrate here that expression of the yeast or monkey metallothionein proteins in the presence of copper suppresses the lactate growth defect and some other phenotypes associated with SOD1-deletion strains, indicating that copper metallothioneins substitute for copper-zinc superoxide dismutase in vivo to protect cells from oxygen toxicity. Consistent with these results, we show that yeast metallothionein mRNA levels are dramatically elevated under conditions of oxidative stress. Furthermore, in vitro assays demonstrate that yeast metallothionein, purified or from whole-cell extracts, exhibits copper-dependent antioxidant activity. Taken together, these data suggest that both yeast and mammalian metallothioneins may play a direct role in the cellular defense against oxidative stress by functioning as antioxidants.
铜锌超氧化物歧化酶催化超氧阴离子歧化为过氧化氢和氧气，被认为在保护细胞免受氧毒性方面发挥重要作用。缺乏由SOD1基因编码的铜锌超氧化物歧化酶的酿酒酵母菌株对氧化应激敏感，并表现出多种生长缺陷，包括对氧气和超氧化物生成药物（如百草枯）过敏。我们发现，除了这些已知表型外，SOD1缺失菌株在含有呼吸碳源乳酸的琼脂上无法生长。我们在此证明，在有铜存在的情况下，酵母或猴金属硫蛋白的表达可抑制乳酸生长缺陷以及与SOD1缺失菌株相关的其他一些表型，这表明铜金属硫蛋白在体内可替代铜锌超氧化物歧化酶来保护细胞免受氧毒性。与这些结果一致，我们表明在氧化应激条件下酵母金属硫蛋白mRNA水平显著升高。此外，体外试验表明，纯化的或来自全细胞提取物的酵母金属硫蛋白具有依赖铜的抗氧化活性。综上所述，这些数据表明酵母和哺乳动物金属硫蛋白都可能通过作为抗氧化剂在细胞防御氧化应激中发挥直接作用。
