期刊
CHEMICAL RESEARCH IN TOXICOLOGY
卷 22, 期 11, 页码 1833-1840出版社
AMER CHEMICAL SOC
DOI: 10.1021/tx900249d
关键词
-
资金
- Marsden Fund
- Health Research Council of New Zealand
Hypothiocyanite is a major oxidant generated by mammalian peroxidases. Although reported to react specifically with thiol groups in biological molecules, a detailed mechanistic study of this reaction has not been conducted. We have investigated the reaction of hypothiocyanous acid/ypothiocyanite with 5-thio-2-nitrobenzoic acid and with reduced glutathione by stopped-flow spectroscopy. The observed bell-shaped pH profile established that the reaction with 5-thio-2-nitrobenzoic acid proceeds via the thiolate and hypothiocyanous acid in the 2.5 < pH < 8 region. The obtained second-order rate constant of the reaction is (1.26 +/- 0.02) x 10(8) M(-1) s(-1), and the effective rate constant at pH 7.4 is (4.37 +/- 0.03) x 10(5) M(-1) s(-1), Analysis of the kinetic data, using a value of 4.38 +/- 0.01 for the pK(a) of 5-thio-2-nitrobenzoic acid thiol (measured independently by spectroscopic analysis), gave a pK(a) of 4.85 +/- 0.01 for hypothiocyanous acid at physiological salt concentration (I = 120 mM; NaCl and phosphate buffer) and 25 degrees C. A second-order rate constant of (8.0 +/- 0.5) x 10(4) M(-1) s(-1) for the reaction of hypothiocyanous acid/hypothiocyanite with reduced glutathione at pH 7.4 was determined. The glutathione data are also consistent with the reaction proceeding via the thiolate and hypothiocyanous acid. Our results demonstrate that hypothiocyanous acid/hypothiocyanite has very high reactivity with thiols and will be short-lived in the presence of physiological concentrations of glutathione and thiol proteins. As the reaction occurs strictly with the thiolate, this oxidant should selectively target proteins containing low pK(a) thiols.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据