Platt Aaron A, Gieseg Steven P
Free Radical Biochemistry Laboratory, Department of Zoology, University of Canterbury, Christchurch, New Zealand.
Redox Rep. 2003;8(2):81-6. doi: 10.1179/135100003125001288.
Studies on plasma and cells exposed to hydroxyl and peroxyl radicals have indicated that there are few inhibitors of protein hydroperoxide formation. We have, however, observed a small variable lag period during bovine serum albumin (BSA) oxidation by 2-2' azo-bis-(2-methyl-propionamidine) HCl (AAPH) generated peroxyl radicals, where no protein hydroperoxide was formed. The addition of free cysteine to BSA during AAPH oxidation also produced a lag phase suggesting protein thiols could inhibit protein hydroperoxide formation. The selective reduction of thiols on BSA by beta-mercaptoethanol treatment caused the appearance of a lag period where no protein hydroperoxide was formed during the AAPH mediated oxidation. Increasing free thiol concentration on the BSA increased the lag period. Protein hydroperoxide formation began when the protein thiol concentration dropped below one thiol per BSA molecule. It is unlikely that the lag period is due to gross structural alteration of the reduced protein since blocking the free thiols with N-ethyl maleimide eliminated the lag in protein hydroperoxide formation. Protein thiols were found to be ineffective in inhibiting hydroxyl radical-mediated protein hydroperoxide formation during X-ray radiolysis. Evidence is given for protein thiol oxidation occurring via a free radical mediated chain reaction with both free cysteine and protein bound thiol. The data suggest that reduced protein thiol groups can inhibit protein hydroperoxide formation by scavenging peroxyl radicals.
对暴露于羟基和过氧自由基的血浆和细胞的研究表明，蛋白质氢过氧化物形成的抑制剂很少。然而，我们观察到在2-2'偶氮双（2-甲基丙脒）盐酸盐（AAPH）产生的过氧自由基氧化牛血清白蛋白（BSA）的过程中，存在一个小的可变延迟期，在此期间没有形成蛋白质氢过氧化物。在AAPH氧化过程中向BSA中添加游离半胱氨酸也产生了一个延迟期，这表明蛋白质硫醇可以抑制蛋白质氢过氧化物的形成。用β-巯基乙醇处理选择性还原BSA上的硫醇会导致出现一个延迟期，在此期间AAPH介导的氧化过程中没有形成蛋白质氢过氧化物。增加BSA上的游离硫醇浓度会延长延迟期。当蛋白质硫醇浓度降至每BSA分子一个硫醇以下时，蛋白质氢过氧化物开始形成。延迟期不太可能是由于还原蛋白的总体结构改变所致，因为用N-乙基马来酰亚胺封闭游离硫醇消除了蛋白质氢过氧化物形成的延迟。发现在X射线辐射分解过程中，蛋白质硫醇在抑制羟基自由基介导的蛋白质氢过氧化物形成方面无效。有证据表明蛋白质硫醇氧化是通过与游离半胱氨酸和蛋白质结合硫醇的自由基介导的链反应发生的。数据表明，还原的蛋白质硫醇基团可以通过清除过氧自由基来抑制蛋白质氢过氧化物的形成。
