Reduction of the Pentavalent Arsenical Dimethylarsinic Acid and the GSTO1 Substrate S-(4-Nitrophenacyl)glutathione by Rat Liver Cytosol: Analyzing the Role of GSTO1 in Arsenic Reduction.
Reduction of the Pentavalent Arsenical Dimethylarsinic Acid and the GSTO1 Substrate S-(4-Nitrophenacyl)glutathione by Rat Liver Cytosol: Analyzing the Role of GSTO1 in Arsenic Reduction.
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DOI：
10.1021/acs.chemrestox.5b00368
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发表时间：
2015-11
影响因子：
4.1
通讯作者：
B. Németi;M. Poór;Z. Gregus
中科院分区：
文献类型：
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作者：
B. Németi;M. Poór;Z. Gregus
二甲基砷酸(DMAS(V))是无机砷的主要尿代谢物。相对无毒的DMAS(V)在体内被还原为毒性更强、硫醇活性更强的二甲基丙氨酸(DMAS(III))。谷胱甘肽S转移酶欧米茄1(GSTO1)可以催化这一毒化步骤，但它在体内或通过组织提取物还原DMAS(V)的作用尚不清楚。因此，我们评估了GSTO1在大鼠肝细胞浆将DMAS(V)还原为DMAS(III)过程中的作用。实验表明，谷胱甘肽(GSH)特异性地支持胞内DMAS(V)的还原，而GSH类似物和GSH结合物，如S-烷基谷胱甘肽和S-(4-硝基苯基)谷胱甘肽(4-NPG；GSTO1特异性底物)，则抑制DMAS(III)的形成。与GSTO1催化DMAs(V)胞浆还原的观点一致的观察包括：(I)发现在DMAS(V)还原胞浆酶上存在GSH结合部位，(Ii)大鼠肝脏胞浆中DMAS(V)和4-NPG还原活性对GSTO1特异性抑制剂KT53和氯甲基荧光素二醋酸酯的反应一致，以及(Iii)在胞浆蛋白的亲和和阴离子交换层析过程中这两种活性的完美结合。关于GSTO1在DMAS(V)胞质还原中的作用，其他观察结果似乎不明确。其中包括DMAS(V)还原活性和GSTO1活性对硫代葡萄糖、三价锑和锌离子的不同敏感性，以及由于自发的硫醇氧化而失去DMAS(V)还原活性的细胞质中保存的GSTO1活性。这些不同的发现可以通过假设GSTO1催化大鼠肝细胞质中DMA(V)和4-NPG的还原来协调；然而，当还原这些底物时，该酶使用不同的位置和/或机制。
Dimethylarsinic acid (DMAs(V)) is the major urinary metabolite of inorganic arsenic. The relatively atoxic DMAs(V) is reduced in the body to the much more toxic and thiol-reactive dimethylarsinous acid (DMAs(III)). Glutathione S-transferase omega 1 (GSTO1) can catalyze this toxification step; however, its role in the reduction of DMAs(V) in vivo or by tissue extracts is unclear. Therefore, we assessed the role of GSTO1 in the reduction of DMAs(V) to DMAs(III) by rat liver cytosol. The experiments revealed that glutathione (GSH) supported the cytosolic DMAs(V) reduction specifically and that GSH analogues and GSH conjugates, such as S-alkylglutathiones and S-(4-nitrophenacyl)glutathione (4-NPG; a GSTO1 specific substrate), inhibited the formation of DMAs(III). Observations in line with the view that GSTO1 catalyzes the cytosolic reduction of DMAs(V) include (i) findings pointing to the presence of a GSH-binding site on the DMAs(V)-reducing cytosolic enzyme, (ii) identical responsiveness of the DMAs(V)- and 4-NPG-reducing activities in rat liver cytosol to the GSTO1 specific inhibitors KT53 and chloromethylfluorescein diacetate, and (iii) perfect coelution of the two activities during affinity and anion exchange chromatography of cytosolic proteins. Other observations appear ambiguous as to the role of GSTO1 in the cytosolic reduction of DMAs(V). These include the different sensitivities of the DMAs(V)-reducing and GSTO1 activities to aurothioglucose, trivalent antimony, and zinc ions, as well as the preserved GSTO1 activity in cytosols whose DMAs(V)-reducing activity was lost due to spontaneous thiol oxidation. These disparate findings may be reconciled by assuming that GSTO1 catalyzes the reduction of both DMAs(V) and 4-NPG in rat liver cytosol; however, the enzyme employs different sites and/or mechanisms when reducing these substrates.