Glutathione (GSH) is the most abundant thiol in mammalian cells and plays a crucial role in maintaining redox cellular homeostasis. The thiols of two GSH molecules can be oxidized to the disulfide GSSG. The cytosolic GSH/GSSG ratio is very high (>100), and its reduction can lead to apoptosis or necrosis, which are of interest in cancer research. Cu^II ions are very efficient oxidants of thiols, but with an excess of GSH, Cu^I_n(GS)_m clusters are formed, in which Cu^I is very slowly reoxidized by O₂ at pH 7.4 and even more slowly at lower pH. Here, the aerobic oxidation of GSH by Cu^II was investigated at different pH values in the presence of the anticancer thiosemicarbazone Dp44mT, which accumulates in lysosomes and induces lysosomal membrane permeabilization in a Cu-dependent manner. The results showed that Cu^II-Dp44mT catalyzes GSH oxidation faster than Cu^II alone at pH 7.4 and hence accelerates the production of very reactive hydroxyl radicals. Moreover, GSH oxidation and hydroxyl radical production by Cu^II-Dp44mT were accelerated at the acidic pH found in lysosomes. To decipher this unusually faster thiol oxidation at lower pH, density functional theory (DFT) calculations, electrochemical and spectroscopic studies were performed. The results suggest that the acceleration is due to the protonation of Cu^II-Dp44mT on the hydrazinic nitrogen, which favors the rate-limiting reduction step without subsequent dissociation of the Cu^I intermediate. Furthermore, preliminary biological studies in cell culture using the proton pump inhibitor bafilomycin A1 indicated that the lysosomal pH plays a role in the activity of Cu^II-Dp44mT.

中文翻译：

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铜催化的谷胱甘肽氧化被抗癌氨基硫脲 Dp44mT 加速，并在较低的 pH 值下进一步促进

谷胱甘肽 (GSH) 是哺乳动物细胞中含量最丰富的硫醇，在维持氧化还原细胞稳态中起着至关重要的作用。两个 GSH 分子的硫醇可以被氧化成二硫化物 GSSG。细胞溶质 GSH/GSSG 比率非常高（>100），其降低可导致细胞凋亡或坏死，这在癌症研究中很重要。Cu ^II离子是硫醇的非常有效的氧化剂，但过量的 GSH 会形成 Cu ^I _n (GS) _m簇，其中 Cu ^I在 pH 7.4 时被 O ₂非常缓慢地再氧化，在较低 pH 时甚至更慢。^{在这里，Cu II}对 GSH 的有氧氧化在抗癌氨基硫脲 Dp44mT 存在下在不同的 pH 值下进行了研究，其在溶酶体中积累并以 Cu 依赖性方式诱导溶酶体膜透化。结果表明，Cu ^{II -Dp44mT 在 pH 7.4 下比单独的 Cu II}更快地催化 GSH 氧化，因此加速了非常活泼的羟基自由基的产生。^{此外，在溶酶体中发现的酸性 pH 值下，Cu II} -Dp44mT 的GSH 氧化和羟基自由基的产生被加速。为了破译这种在较低 pH 值下异常快速的硫醇氧化，进行了密度泛函理论 (DFT) 计算、电化学和光谱研究。结果表明加速是由于Cu ^{II的质子化}-Dp44mT 在肼氮上，这有利于限速还原步骤，而不会随后解离 Cu ^I中间体。此外，使用质子泵抑制剂巴弗洛霉素 A1 在细胞培养中进行的初步生物学研究表明，溶酶体 pH 在 Cu ^II -Dp44mT 的活性中起作用。