Di Simplicio P, Cheeseman K H, Slater T F
Dept. of Environmental Biology, Faculty of Science, University of Siena, Italy.
Free Radic Res Commun. 1991;14(4):253-62. doi: 10.3109/10715769109088954.
The reactivity of the SH group of bovine serum albumin (BSA) towards free radicals generated by several different systems including gamma-radiolysis and hydrogen peroxide/metal salt mixtures was investigated. On exposure of BSA (1 mg/ml and 5 mg/ml) to HO. radicals generated radiolytically the protein-SH concentration was found to decrease in a dose-dependent manner. At 40 mg/ml albumin no loss of SH was observed. O2-. and HO2. radicals were much less aggressive towards the SH group. The effect of divalent metal salts (copper or iron) plus hydrogen peroxide was studied separately and in combination. H2O2 alone caused a decrease in SH group concentration the rate of which was not decreased by the presence of desferrioxamine and so was apparently not due to reactions catalysed by adventitious metal ions. Copper alone caused a dose-dependent decrease in SH group concentration and the mixture of the two agents caused a greater loss of SH than each separate component. However, this latter effect was again resistant to the effects of desferrioxamine. The SH group of BSA was only moderately sensitive to the presence of ferrous iron alone and in a system containing both ferrous iron and H2O2 rates of SH oxidation were obtained that were identical to those obtained with H2O2 alone. Desferrioxamine again did not alter the rate of SH oxidation in these experiments. We suggest that the highly reactive free radical HO. is not able to reach and to oxidize the SH group of BSA when generated by metal/H2O2 mixtures, in contrast to HO. generated radiolytically. Less reactive radicals and non-radical species such as H2O2 have more potential for doing so.
研究了牛血清白蛋白（BSA）的巯基（SH）对几种不同体系产生的自由基的反应性，这些体系包括γ辐射分解以及过氧化氢/金属盐混合物。将BSA（1mg/ml和5mg/ml）暴露于辐射分解产生的羟基自由基（HO·）时，发现蛋白质的SH浓度呈剂量依赖性降低。在白蛋白浓度为40mg/ml时，未观察到SH的损失。超氧阴离子自由基（O2-·）和过氧化氢自由基（HO2·）对SH基团的攻击性要小得多。分别研究了二价金属盐（铜或铁）与过氧化氢单独作用及联合作用的效果。单独的过氧化氢会导致SH基团浓度降低，去铁胺的存在并不会降低其降低速率，所以这显然不是由偶然存在的金属离子催化的反应所致。单独的铜会导致SH基团浓度呈剂量依赖性降低，两种试剂的混合物导致的SH损失比每种单独成分都要大。然而，后一种效应同样不受去铁胺的影响。BSA的SH基团仅对单独存在的亚铁离子中度敏感，在同时含有亚铁离子和过氧化氢的体系中，SH氧化速率与单独使用过氧化氢时相同。在这些实验中，去铁胺同样没有改变SH的氧化速率。我们认为，与辐射分解产生的HO·相比，由金属/过氧化氢混合物产生的高活性自由基HO·无法到达并氧化BSA的SH基团。活性较低的自由基和非自由基物质（如过氧化氢）更有这样的可能性。
