METHIONINE SULFOXIDE REDUCTASE

蛋白质暴露在氧气中，尤其是暴露在还原的氧气中 化合物，如过氧化氢和羟基自由基，允许 蛋白质分子上敏感部位的氧化。对敏感的人 网站，蛋氨酸的硫磺特别容易受到攻击。一个 蛋氨酸亚麻酸还原酶可以逆转这种氧化和 它已被证明在氧化损伤的持续修复中起着重要作用。 受损的蛋白质。分析表明，这种酶的活性在 费舍尔344只大鼠随着年龄的增长逐渐减少，尽管不是很明显。 它还表明，这种酶分布广泛，是 在大肠杆菌、酿酒酵母、牛肝和 人类细胞(细胞培养)。酿酒酵母基因已被克隆并 插入到允许过量生产酶的质粒中。什么时候 缺乏蛋氨酸亚砜还原酶的a突变体被给予 含有该基因的质粒，其表型类似于野生型酵母。 与大肠杆菌中的酶活性一样，酵母菌的活性最高 在原木晚期和静止期培养中强烈表达。这 这种表达似乎与受损的蛋氨酸可能 是最普遍的，当细胞暴露时需要修复 最长的氧气。蛋白结合型蛋氨酸亚砜的Km (使用模型化合物N-DABSYL-亚砜)在微摩尔中 范围：酵母菌15.3，牛肉31.8，大肠杆菌120。

Exposure of proteins to oxygen and, especially to reduced oxygen compounds, such as hydrogen peroxide and hydroxyl radical, permits the oxidation of sensitive sites on the protein molecules. Of the sensitive sites, the sulfur of methionine is particularly subject to attack. An enzyme, methionine sulfoxide reductase, can reverse this oxidation and it has been shown to be a player in the continuing repair of oxidatively damaged proteins. Assays have shown that activity of this enzyme in Fisher 344 rats gradually, although not dramatically, declines with age. It has been shown, also, that the enzyme is widely distributed, being found in Escherichia coli, Saccharomyces cerevisiae, beef liver, and human cells (cell culture). The S. cerevisiae gene has been cloned and inserted in a plasmid which permits over-production of the enzyme. When the a mutant, lacking methionine sulfoxide reductase, is given the plasmid containing the gene, the phenotype resembles wild-type yeast. Like the enzyme activity in E. coli, the yeast activity is most vigorously expressed in late log and stationary phase cultures. This expression seems consistent with the idea that damaged methionines may be most prevalent and in need of repair when the cells have been exposed the longest to oxygen. The Km for protein-bound methionine sulfoxide (using the model compound, N-DABSYL-sulfoxide) is in the micromolar range: 15.3 for yeast, 31.8 for beef, and 120 for E. coli.