The high content of glutathione (GSH) in the lens is believed to protect thiols in structural proteins and enzymes for proper biological functions. The lens has both biosynthetic and regenerating systems for GSH to maintain its large pool size. However, ageing lenses or lenses under oxidative stress show an extensively diminished size of GSH pool with some protein thiols being S-thiolated by oxidized non-protein thiols to form protein-thiol mixed disulfides, either as protein-S-S-glutathione (PSSG) or protein-S-S-cysteine (PSSC) or protein-S-S-gamma-glutamylcysteine. It was shown in an H(2)O(2)-induced cataract model that PSSG formation precedes a cascade of events before cataract formation, starting with protein disulfide crosslinks, protein solubility loss and high molecular weight aggregation. Furthermore, this early oxidative damage in protein thiols can be spontaneously reversed in H(2)O(2) pretreated lenses if the oxidant is removed in time. This dethiolation process appears to have mediated through a redox-regulating enzyme, thioltransferase (TTase), which is ubiquitously present in microbial, plant and animal tissues, including the lens. The GSH-dependent, low molecular weight (11.8 kDa) cytosolic enzyme plays an important role in oxidative defense and can modulate key metabolic enzymes in the glycolytic pathway. The enzyme repairs oxidatively damaged proteins/enzymes through its unique catalytic site with a vicinal cysteine moiety, which can specifically dethiolate protein-S-S-glutathione and restore protein free SH groups for proper enzymatic or protein functions. Most importantly, it has been demonstrated that thioltransferase has a remarkable resistance to oxidation (H(2)O(2)) in cultured human and rabbit lens epithelial cells under oxidative stress conditions when other oxidation defense systems of GSH peroxidase and GSH reductase are severely inactivated. A second repair enzyme, thioredoxin (TRx), which is NADPH-dependent, is widely found in many lower and higher life forms of life. It can dethiolate protein disulfides and thus is an extremely important regulator for redox homeostasis in the cells. Thioredoxin has been recently found in the lens and has been shown to participate in the repair process of oxidatively damaged lens proteins/enzymes. These two enzymes may work synergistically to regulate and repair thiols in lens proteins and enzymes, keeping a balanced redox potential to maintain the function of the lens.

中文翻译：

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镜头中的氧化还原调节。

晶状体中高含量的谷胱甘肽（GSH）被认为可以保护结构蛋白和酶中的硫醇，以实现适当的生物学功能。晶状体具有用于GSH的生物合成和再生系统，以维持其较大的池大小。但是，老化的晶状体或处于氧化应激状态的晶状体显示GSH池的大小大大减小，一些蛋白硫醇被氧化的非蛋白硫醇S-硫醇化形成蛋白-硫醇混合二硫键，即蛋白-SS-谷胱甘肽（PSSG）或蛋白质-SS-半胱氨酸（PSSC）或蛋白质-SS-γ-谷氨酰半胱氨酸。在H（2）O（2）诱发的白内障模型中显示，PSSG的形成先于白内障形成之前的一系列事件，从蛋白质二硫键交联，蛋白质溶解度损失和高分子量聚集开始。此外，如果及时清除氧化剂，可以在H（2）O（2）预处理的镜片中自发逆转这种蛋白质硫醇的早期氧化损伤。该脱硫过程似乎是通过氧化还原调节酶巯基转移酶（TTase）介导的，该酶普遍存在于微生物，植物和动物组织（包括晶状体）中。GSH依赖的低分子量（11.8 kDa）胞质酶在氧化防御中起重要作用，并且可以调节糖酵解途径中的关键代谢酶。该酶通过其邻近的半胱氨酸部分的独特催化位点修复氧化损伤的蛋白质/酶，该酶可以特异性地使蛋白质-SS-谷胱甘肽脱硫并恢复不含蛋白质的SH基团，以实现适当的酶或蛋白质功能。最重要的是，已经证明，当其他GSH过氧化物酶和GSH还原酶的氧化防御系统被严重失活时，硫醇转移酶对培养的人和兔晶状体上皮细胞在氧化应激条件下具有显着的抗氧化性（H（2）O（2））。NADPH依赖的第二种修复酶，硫氧还蛋白（TRx），在许多较低和较高的生命形式中得到广泛发现。它可以使蛋白质二硫键脱硫，因此是细胞中氧化还原稳态的重要调节剂。硫氧还蛋白最近在晶状体中发现，并已显示出参与氧化损伤的晶状体蛋白/酶的修复过程。这两种酶可以协同作用来调节和修复晶状体蛋白质和酶中的硫醇，从而保持平衡的氧化还原电位以维持晶状体的功能。