Suh Jung H, Zhu Ben-Zhan, deSzoeke Evan, Frei Balz, Hagen Tory M
Department of Biochemistry and Biophysics, Oregon State University, Corvallis, Oregon 97331, USA.
Redox Rep. 2004;9(1):57-61. doi: 10.1179/135100004225003923.
Alpha-lipoic acid (LA) and its reduced form, dihydrolipoic acid (DHLA), have been suggested to chelate transition metal ions and, hence, mitigate iron- and copper-mediated oxidative stress in biological systems. However, it remains unclear whether LA and DHLA chelate transition metal ions in a redox-inactive form, and whether they remove metal ions from the active site of enzymes. Therefore, we investigated the effects of LA and DHLA on iron- or copper-catalyzed oxidation of ascorbate, a sensitive assay for the redox activity of these metal ions. We found that DHLA, but not LA, significantly inhibited ascorbate oxidation mediated by Fe(III)-citrate, suggesting that reduced thiols are required for iron binding. DHLA also strongly inhibited Cu(II)(histidine)(2)-mediated ascorbate oxidation in a concentration-dependent manner, with complete inhibition at a DHLA:Cu(II) molar ratio of 3:1. In contrast, no inhibition of copper-catalyzed ascorbate oxidation was observed with LA. To investigate whether LA and DHLA remove copper or iron from the active site of enzymes, Cu,Zn superoxide dismutase and the iron-containing enzyme aconitase were used. We found that neither LA nor DHLA, even at high, millimolar concentrations, altered the activity of these enzymes. Our results suggest that DHLA chelates and inactivates redox-active transition metal ions in small-molecular, biological complexes without affecting iron- or copper-dependent enzyme activities.
α-硫辛酸（LA）及其还原形式二氢硫辛酸（DHLA）被认为可以螯合过渡金属离子，从而减轻生物系统中由铁和铜介导的氧化应激。然而，目前尚不清楚LA和DHLA是否以氧化还原非活性形式螯合过渡金属离子，以及它们是否能从酶的活性位点去除金属离子。因此，我们研究了LA和DHLA对铁或铜催化的抗坏血酸氧化的影响，这是一种检测这些金属离子氧化还原活性的灵敏方法。我们发现，DHLA而非LA能显著抑制柠檬酸铁（III）介导的抗坏血酸氧化，这表明铁结合需要还原型硫醇。DHLA还以浓度依赖的方式强烈抑制铜（II）（组氨酸）2介导的抗坏血酸氧化，当DHLA与铜（II）的摩尔比为3:1时完全抑制。相比之下，LA未观察到对铜催化的抗坏血酸氧化有抑制作用。为了研究LA和DHLA是否能从酶的活性位点去除铜或铁，我们使用了铜锌超氧化物歧化酶和含铁酶乌头酸酶。我们发现，即使在毫摩尔的高浓度下，LA和DHLA都不会改变这些酶的活性。我们的结果表明，DHLA能螯合并使小分子生物复合物中的氧化还原活性过渡金属离子失活，而不影响铁或铜依赖的酶活性。
