METHIONINE SULFOXIDE REDUCTASE

暴露在氧气和活性氧物种中 (羟基、超氧化物、过氧化氢等) 允许蛋白质分子上的敏感部位氧化。的 敏感部位，蛋氨酸的硫磺尤其容易受到 进攻。这种名为蛋氨酸亚砜还原酶的酶可以还原 氧化蛋氨酸，从而修复一些损伤。我们 以前已经显示了酶活性的广泛分布 在自然界中。多肽连接的蛋氨酸亚砜可以被还原 在常规检测中以二硫苏糖醇为代价，或NADPH可以 通过硫氧还蛋白和硫氧还蛋白提供还原动力 还原酶。除了碳的手性中心外，还有一个 蛋氨酸在硫磺上产生额外的中心 亚硫醚就形成了。蛋氨酸亚麻酸还原酶只利用 “S”式的亚砜为底物，而不是“r”式。这 特异性似乎适用于来自酵母菌的酶 Cerevisiae和Escherichia colias。很可能是因为 专一性是这类酶的一般特性。酵母细胞在 已经被消除的还原酶更不能承受 氧化应激(如接触过氧化氢)比 野生型细胞。包含多个拷贝的基因的细胞 还原酶的生长很像野生型细胞。

Exposure to oxygen and reactive oxygen species (hydroxyl radical, superoxide, hydrogen peroxide, and the like) permits the oxidation of sensitive sites on protein molecules. Of sensitive sites, the sulfur of methionine is particularly subject to attack. The enzyme, methionine sulfoxide reductase, can reduce oxidized methionine and thereby repair some of the damage. We have previously shown the wide distribution of the enzymic activity in nature. The peptide-linked methionine sulfoxide can be reduced at the expense of dithiothreitol in routine assays, or NADPH can provide the reducing power via thioredoxin and thioredoxin reductase. In addition to the chiral center at the carbon, an additional center is generated at the sulfur when methionine sulfoxide is formed. Methionine sulfoxide reductase utilizes only the "s" form of the sulfoxide as substrate, not the "r" form. This specificity appears to apply to the enzyme from Saccharomyces cerevisiae and to that from Escherichia coli. It is probable that the specificity is a general property of such enzymes. Yeast cells in which the reductase has been eliminated are less able to withstand oxidative stress (such as exposure to hydrogen peroxide) than are wild-type cells. Cells which contain multiple copies of the gene for the reductase grow much like the wild-type cells.