Mechanism of tryptophan oxidation by some inorganic radical-anions: a pulse radiolysis study
Mechanism of tryptophan oxidation by some inorganic radical-anions: a pulse radiolysis study
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一些无机自由基阴离子氧化色氨酸的机制：脉冲放射分解研究
DOI：
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发表时间：
1976
期刊：
影响因子：
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通讯作者：
R. Cundall
中科院分区：
文献类型：
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作者：
M. L. Posener;G. Adams;P. Wardman;R. Cundall
卤素离子、硫氰酸根离子、碳酸根离子和亚硒酸根离子被羟基自由基氧化，产生自由基阴离子，这些自由基阴离子本身氧化氨基酸，如色氨酸和酪氨酸。在中性和碱性溶液中，Br-2、（SCN）-2、CO-3和亚硒酸根自由基氧化色氨酸（TrpH）的自由基产物具有相似的光谱和动力学性质。在pH = 1.3下观察到的色氨酸自由基的光谱位移和衰减动力学表明，Br-2和（SCN）-2氧化TrpH得到一个自由基，该自由基质子化（pKa= 4.3），在pH = 1.3时带单电荷。由亚硒酸根的氧化TrpH的产物的吸收的不同亲质子行为表明，在这种情况下，产生一个以上的物种。质子化自由基TrpH+与SCN-反应，使得（SCN）-2对TrpH的反应性明显丧失，特别是在低pH、高[SCN-]和低[TrpH]下。（SCN）-2/TrpH反应的动力学模型预测了（SCN）-2的平衡浓度随[H+]、[TrpH]和[SCN-]的变化。实验数据与模型雅阁，并能求出反应的平衡常数。
Oxidation of halide, thiocyanate, carbonate and selenite ions by hydroxyl radicals yields radicalanions which themselves oxidise amino-acids such as tryptophan and tyrosine. The free-radical product(s) of oxidation of tryptophan (TrpH) by Br–2, (SCN)–2, CO–3 and a selenite free radical have similar spectral and kinetic properties in neutral and alkaline solutions. The spectral shifts and decay kinetics of the tryptophan free-radical observed at pH ∼ 3 show that oxidation of TrpH by Br–2 and (SCN)–2 gives a radical which protonates (pKa= 4.3) and which is singly charged at pH ∼ 3. The different prototropic behaviour of the absorption of the product of oxidation of TrpH by the selenite radical suggests that in this case, more than one species is produced. The protonated free radical TrpH+ reacts with SCN– so that there is an apparent loss of reactivity of (SCN)–2 towards TrpH, especially at low pH, high [SCN–] and low [TrpH]. A kinetic model for the (SCN)–2/TrpH reaction predicts a variation of the equilibrium concentration of (SCN)–2 with [H+], [TrpH] and [SCN–]. The experimental data are in accord with the model and enable the equilibrium constants of the reactions to be obtained.