Harel S, Kanner J
Agricultural Research Organization, Volcani Center, Bet Dagan, Israel.
Free Radic Res Commun. 1988;5(1):21-33. doi: 10.3109/10715768809068555.
The oxidation of 2-keto-4-thiomethyl butyric acid (KTBA) and methionine to ethylene has been used to evaluate generation of ferryl species or hydroxyl radicals by H2O2-activated haemproteins or free ferric ions. Hydrogen peroxide was generated by a glucose oxidase-glucose system at a rate of 1 microM/min. Free ferric in the presence of H2O2 oxidizes KTBA, and this was highly inhibited by hydroxyl radical scavengers, caeruloplasmin, superoxide dismutase (SOD) and EDTA. However, when metmyoglobin, methaemoglobin (MtHb) or horseradish peroxidase (HRP) were tested in the same model system, hydroxyl radical scavengers suppressed partially KTBA oxidation and caeruloplasmin, SOD and EDTA failed to inhibit the reaction. Cytochrome-c was found to be a weak promoter of KTBA oxidation in the presence of H2O2. Methionine was oxidized to ethylene by an active system which generates hydroxyl radicals, but not by H2O2-activated metmyoglobin. Ferric ions chelated to membranes or ADP in the presence of H2O2 generated enzymatically, initiated membranal lipid peroxidation only in the presence of ascorbic acid, and this was inhibited by EDTA. In contrast, metmyoglobin and methaemoglobin activated by H2O2 generated by the same system, initiated membranal lipid peroxidation and this was not inhibited by EDTA. It is concluded that ferryl and not HO. is the main oxidant in systems containing myoglobin and haemoglobin activated by low concentrations of H2O2.
已利用2-酮-4-硫代甲基丁酸（KTBA）和蛋氨酸氧化生成乙烯，来评估过氧化氢激活的血红素蛋白或游离铁离子产生的高铁物种或羟基自由基。葡萄糖氧化酶-葡萄糖系统以1微摩尔/分钟的速率产生过氧化氢。过氧化氢存在下的游离铁离子会氧化KTBA，而羟基自由基清除剂、铜蓝蛋白、超氧化物歧化酶（SOD）和乙二胺四乙酸（EDTA）可高度抑制这种氧化。然而，在同一模型系统中测试高铁肌红蛋白、高铁血红蛋白（MtHb）或辣根过氧化物酶（HRP）时，羟基自由基清除剂只能部分抑制KTBA氧化，铜蓝蛋白、SOD和EDTA无法抑制该反应。发现在过氧化氢存在下，细胞色素c是KTBA氧化的弱促进剂。蛋氨酸可被产生羟基自由基的活性系统氧化为乙烯，但不能被过氧化氢激活的高铁肌红蛋白氧化。在酶促产生过氧化氢的情况下，与膜或二磷酸腺苷（ADP）螯合的铁离子仅在存在抗坏血酸时才引发膜脂质过氧化，且这种过氧化可被EDTA抑制。相反，同一系统产生的过氧化氢激活的高铁肌红蛋白和高铁血红蛋白会引发膜脂质过氧化，且这种过氧化不受EDTA抑制。得出的结论是，在低浓度过氧化氢激活的含有肌红蛋白和血红蛋白的系统中，主要氧化剂是高铁物种而非羟基自由基。
