Rhee Sue Goo, Chae Ho Zoon, Kim Kanghwa
Laboratory of Cell Signaling, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Free Radic Biol Med. 2005 Jun 15;38(12):1543-52. doi: 10.1016/j.freeradbiomed.2005.02.026. Epub 2005 Mar 24.
The observation that purified yeast glutamine synthetase is rapidly inactivated in a thiol-containing buffer yet retains activity in crude extracts containing the same thiol led to our discovery of an enzyme that protects against oxidation in a thiol-containing system. This novel antioxidant enzyme was shown to reduce hydroperoxides and, more recently, peroxynitrite with the use of electrons provided by a physiological thiol like thioredoxin. It defined a family of proteins, present in organisms from all kingdoms, that was named peroxiredoxin (Prx). All Prx enzymes contain a conserved Cys residue that undergoes a cycle of peroxide-dependent oxidation and thiol-dependent reduction during catalysis. Mammalian cells express six isoforms of Prx (Prx I to VI), which are classified into three subgroups (2-Cys, atypical 2-Cys, and 1-Cys) based on the number and position of Cys residues that participate in catalysis. The relative abundance of Prx enzymes in mammalian cells appears to protect cellular components by removing the low levels of peroxides produced as a result of normal cellular metabolism. During catalysis, the active site cysteine is occasionally overoxidized to cysteine sulfinic acid. Contrary to the general belief that oxidation to the sulfinic state is an irreversible process in cells, studies on the fate of the overoxidized Prx species revealed a mechanism by which the catalytically active thiol form is recovered. This sulfinic reduction is a slow, ATP-dependent process that is specific to 2-Cys Prx isoforms. This reversible overoxidation may represent an adaptation unique to eukaryotic cells that accommodates the intracellular messenger function of H(2)O(2), but experimental validation of such speculation is yet to come.
纯化的酵母谷氨酰胺合成酶在含硫醇的缓冲液中会迅速失活，但在含有相同硫醇的粗提物中却能保持活性，这一观察结果促使我们发现了一种在含硫醇系统中防止氧化的酶。这种新型抗氧化酶被证明能利用硫氧还蛋白等生理性硫醇提供的电子来还原氢过氧化物，最近还能还原过氧亚硝酸盐。它定义了一类存在于所有生物界生物体中的蛋白质家族，被命名为过氧化物酶（Prx）。所有Prx酶都含有一个保守的半胱氨酸残基，在催化过程中经历一个依赖过氧化物的氧化和依赖硫醇的还原循环。哺乳动物细胞表达六种Prx同工型（Prx I至VI），根据参与催化的半胱氨酸残基的数量和位置，它们被分为三个亚组（2-半胱氨酸、非典型2-半胱氨酸和1-半胱氨酸）。哺乳动物细胞中Prx酶的相对丰度似乎通过去除正常细胞代谢产生的低水平过氧化物来保护细胞成分。在催化过程中，活性位点的半胱氨酸偶尔会过度氧化为半胱氨酸亚磺酸。与一般认为氧化为亚磺酸状态在细胞中是一个不可逆过程的观点相反，对过度氧化的Prx物种命运的研究揭示了一种回收催化活性硫醇形式的机制。这种亚磺酸还原是一个缓慢的、依赖ATP的过程，是2-半胱氨酸Prx同工型所特有的。这种可逆的过度氧化可能代表了真核细胞特有的一种适应方式，以适应H₂O₂的细胞内信使功能，但这种推测的实验验证尚未到来。
