Esworthy R S, Chu F F, Geiger P, Girotti A W, Doroshow J H
Department of Medical Oncology and Therapeutics Research, City of Hope National Medical Center, Duarte, California 91010.
Arch Biochem Biophys. 1993 Nov 15;307(1):29-34. doi: 10.1006/abbi.1993.1555.
We studied enzyme kinetics parameters of plasma glutathione peroxidase (GSHPx-P) and the major cellular enzyme, GSHPx-1, for the substrates, H2O2, linoleic acid hydroperoxide (LinOOH), and glutathione (GSH). The major objectives were to determine whether the relatively slow GSHPx-P enzyme had a lower reactivity with hydroperoxides or with GSH and to identify favored hydroperoxide substrates. The rate constants describing the reactivity of human GSHPx-P and human GSHPx-1 with LinOOH and H2O2 are in the same range; GSHPx-P is more reactive with LinOOH and GSHPx-1 is more reactive with H2O2. GSHPx-P also has a low level of reducing activity toward cholesterol 7 alpha-OOH and no detectable activity with the 5 alpha-OOH isomer in contrast to phospholipid hydroperoxide glutathione peroxidase (PHGPx) which readily reduced both isomers. GSHPx-P catalytic activity toward phospholipid hydroperoxides is demonstrable in the absence of detergents, enhanced at low concentrations by deoxycholate, and strongly inhibited by Triton X-100 and incorporation into liposomes. These properties are the opposite of PHGPx. These results suggest that GSHPx-P largely lacks the membrane interfacial properties of PHGPx. GSHPx-P exhibits a smaller GSH rate constant than GSHPx-1. This property partially explains the slower turnover of GSHPx-P with several hydroperoxide substrates; the low reactivity with GSH is not consistent with efficient GSHPx function in the bulk plasma volume. GSHPx-P kinetic properties suggest that it would function best as a free fatty acid hydroperoxidase in GSH-rich microenvironments. Minimally, the secretion of reduced enzyme would permit it to scavenge free fatty acid hydroperoxides.
我们研究了血浆谷胱甘肽过氧化物酶（GSHPx-P）以及主要的细胞内酶GSHPx-1针对底物过氧化氢（H2O2）、亚油酸氢过氧化物（LinOOH）和谷胱甘肽（GSH）的酶动力学参数。主要目的是确定相对较慢的GSHPx-P酶对氢过氧化物或GSH的反应性是否较低，并确定其偏好的氢过氧化物底物。描述人GSHPx-P和人GSHPx-1与LinOOH和H2O2反应性的速率常数处于同一范围；GSHPx-P与LinOOH的反应性更强，而GSHPx-1与H2O2的反应性更强。与磷脂氢过氧化物谷胱甘肽过氧化物酶（PHGPx）能轻易还原两种异构体相反，GSHPx-P对胆固醇7α-OOH的还原活性水平较低，对5α-OOH异构体没有可检测到的活性。在没有去污剂的情况下，GSHPx-P对磷脂氢过氧化物具有催化活性，脱氧胆酸盐在低浓度时可增强该活性，而Triton X-100和脂质体包埋则会强烈抑制该活性。这些特性与PHGPx相反。这些结果表明，GSHPx-P在很大程度上缺乏PHGPx的膜界面特性。GSHPx-P表现出比GSHPx-1更小的GSH速率常数。这一特性部分解释了GSHPx-P与几种氢过氧化物底物反应时周转较慢的原因；与GSH的低反应性与在大量血浆中高效发挥GSHPx功能不一致。GSHPx-P的动力学特性表明，在富含GSH的微环境中，它作为游离脂肪酸氢过氧化物酶发挥的功能最佳。至少，分泌还原型酶将使其能够清除游离脂肪酸氢过氧化物。
