Madej Edyta, Wardman Peter
University of Oxford, Gray Cancer Institute, Mount Vernon Hospital, Northwood, Middlesex, UK.
Arch Biochem Biophys. 2007 Jun 1;462(1):94-102. doi: 10.1016/j.abb.2007.03.002. Epub 2007 Mar 28.
The oxidizing power of the thiyl radical (GS*) produced on oxidation of glutathione (GSH) was determined as the mid-point electrode potential (reduction potential) of the one-electron couple E(m)(GS*,H+/GSH) in water, as a function of pH over the physiological range. The method involved measuring the equilibrium constants for electron-transfer equilibria with aniline or phenothiazine redox indicators of known electrode potential. Thiyl and indicator radicals were generated in microseconds by pulse radiolysis, and the position of equilibrium measured by fast kinetic spectrophotometry. The electrode potential E(m)(GS*,H+/GSH) showed the expected decrease by approximately 0.06 V/pH as pH was increased from approximately 6 to 8, reflecting thiol/thiolate dissociation and yielding a value of the reduction potential of GS*=0.92+/-0.03 V at pH 7.4. An apparently almost invariant potential between pH approximately 3 and 6, with potentials significantly lower than expected, is ascribed at least in part to errors arising from radical decay during the approach to the redox equilibrium and slow electron transfer of thiol compared to thiolate.
谷胱甘肽（GSH）氧化产生的硫自由基（GS*）的氧化能力，被确定为水中单电子对E(m)(GS*,H+/GSH)的中点电极电位（还原电位），它是生理范围内pH值的函数。该方法包括测量与已知电极电位的苯胺或吩噻嗪氧化还原指示剂的电子转移平衡的平衡常数。硫自由基和指示剂自由基通过脉冲辐解在微秒内产生，平衡位置通过快速动力学分光光度法测量。当pH值从约6增加到8时，电极电位E(m)(GS*,H+/GSH)呈现出预期的下降，约为0.06 V/pH，这反映了硫醇/硫醇盐的解离，并在pH 7.4时得出GS*的还原电位值为0.92±0.03 V。在pH约3至6之间，电位明显低于预期且几乎不变，这至少部分归因于在接近氧化还原平衡过程中自由基衰变产生的误差，以及与硫醇盐相比硫醇的电子转移缓慢。
