Kinetics of the reactions of hypochlorous acid and amino acid chloramines with thiols, methionine, and ascorbate
Kinetics of the reactions of hypochlorous acid and amino acid chloramines with thiols, methionine, and ascorbate
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DOI：
10.1016/s0891-5849(00)00506-2
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发表时间：
2001-03-01
影响因子：
7.4
通讯作者：
Winterbourn, CC
中科院分区：
文献类型：
--
作者：
Peskin, AV;Winterbourn, CC
次氯酸和氯胺对硫醇的氧化是一种有利的反应，可能与暴露于中性粒细胞氧化剂的细胞的调节或信号通路的改变有关。为了建立这种变化的机制，有必要了解这些氧化剂与其他清除剂相比是否对不同的硫醇具有选择性。我们使用停流和竞争动力学相结合的方法，测量了氨基酸氯胺与一系列硫醇、蛋氨酸和抗坏血酸反应的速率常数。对于HOCl，速率常数太快，无法用我们的系统直接测量，相对于还原的谷胱甘肽的值是通过与蛋氨酸的竞争来确定的。牛磺酸氯胺与5-硫代-2-硝基苯甲酸、谷胱甘肽、蛋氨酸和抗坏血酸在pH 7.4时的反应速率常数分别为970、115、39和13M~(-1)S。10个硫醇的值变化了20倍，并且与硫醇的pK(A)成反比。甘氨酸和N-α-乙酰赖氨酸的氯胺的速率常数也表现出这些关系。反应速率随pH值的降低而增加，表明反应机理与酸催化有关。对于次氯酸，与5-硫代-2-硝基苯甲酸、谷胱甘肽、半胱氨酸和大多数其他硫醇的反应速度非常相似。相对反应性变化小于5，且不依赖于硫醇PK(A)。氯胺对不同的细胞硫醇具有潜在的选择性，这取决于它们的pK(A)。要使HOCl具有选择性，其他因素必须是重要的，否则其反应可能是次要的，而不是氯胺的形成。(C)2001年爱思唯尔科学公司。
Thiol oxidation by hypochlorous acid and chloramines is a favorable reaction and may be responsible for alterations in regulatory or signaling pathways in cells exposed to neutrophil oxidants. In order to establish the mechanism for such changes, it is necessary to appreciate whether these oxidants are selective for different thiols as compared with other scavengers. We have measured rate constants for reactions of amino acid chloramines with a range of thiols, methionine, and ascorbate, using a combination of stopped-flow and competitive kinetics. For HOCl, rate constants are too fast to measure directly by our system and values relative to reduced,glutathione were determined by competition with methionine. For taurine chloramine, the rate constants for reaction with 5-thio-2-nitrobenzoic acid, GSH, methionine, and ascorbate at pH 7.4 were 970, 115, 39, and 13 M-1 s(-1), respectively. Values for 10 thiols varied by a factor of 20 and showed an inverse relationship to the pK(a) of the thiol group. Rate constants for chloramines of glycine and N-alpha -acetyl-lysine also showed these relationships. Rates increased with decreasing pH, suggesting a mechanism involving acid catalysis. For hypochlorous acid, rates of reaction with 5-thio-2-nitrobenzoic acid, GSH, cysteine, and most of the other thiols were very similar. Relative reactivities varied by less than 5 and there was no dependence on thiol pK(a). Chloramines have the potential to be selective for different cellular thiols depending on their pK(a). For HOCl to be selective, other factors must be important, or its reactions could be secondary to chloramine formation. (C) 2001 Elsevier Science Inc.