Stopped-flow kinetic study of the reaction of ascorbic acid with peroxynitrite.
Stopped-flow kinetic study of the reaction of ascorbic acid with peroxynitrite.
复制标题
抗坏血酸与过氧亚硝酸盐反应的停流动力学研究。
DOI：
10.1006/abbi.1995.1435
复制
发表时间：
1995
影响因子：
3.9
通讯作者：
William A. Pryor
中科院分区：
文献类型：
--
作者：
Giuseppe L. Squadrito;Xia Jin;William A. Pryor
提出了过氧亚硝酸根氧化抗坏血酸的新机理。我们的机理涉及抗坏血酸与基态过亚硝酸(HOONO)和反应性中间体(HOONO*)的反应；反应性中间体被假定在HOONO的衰变过程中形成硝酸盐。在生理pH下，抗坏血酸单阴离子(AH-)是主要的抗坏血酸物种。过亚硝酸根与AH-反应的观察到的过亚硝酸根衰变速率常数(KOBS)与AH-的关系图显示出两个区域，一个是线性的，一个是曲线的。在H-浓度较高的线性区域，反应以HOONO和AH-的双分子反应为主。在较低的AH-浓度下，这种双分子反应变慢，与HOONO和HOONO*的反应产生观察到的曲率。对数据的分析得到了AH-与HOONO反应的速率常数之比(K2*)和HOONO与硝酸盐的衰变(KN)，得到K2*/KN=3158+/-505M-1，以及AH-与HOONO反应的速率常数(K2)，K2=236+/-14M-1 S-1。抗坏血酸表现出比蛋氨酸或2-酮-4-硫甲基丁酸更高的对HOONO*的选择性，这两种底物对HOONO和HOONO*的反应已被报道。抗坏血酸与过亚硝酸根反应的生物相关性从速率常数和在生物体系中常见的AH-的浓度方面进行了讨论；抗坏血酸可以与HOONO*反应，尽管与基态HOONO的反应可能太慢而不能在体内发生。
A new mechanism is presented for the oxidation of ascorbate by peroxynitrite. Our mechanism involves the reaction of ascorbate both with ground-state peroxynitrous acid (HOONO) and with a reactive intermediate (HOONO*); the reactive intermediate is postulated to be formed in the decay of HOONO to form nitrate. At physiological pH, the ascorbate monoanion (AH-) is the predominant ascorbate species. The plot of the observed rate constant for peroxynitrite decay (kobs) vs AH- for the reaction of peroxynitrite with AH- shows two regions, one linear and one curved. In the linear region, which involves high AH- concentrations, the reaction is dominated by the bimolecular reaction between HOONO and AH-. At lower AH- concentrations, this bimolecular reaction slows and reactions with both HOONO and HOONO* produce the observed curvature. Analysis of the data leads to the estimation of the ratio of rate constants for the reaction of AH- with HOONO* (k2*) and the decay of HOONO to nitrate (kN), giving the value of k2*/kN = 3158 +/- 505 M-1; and of the rate constant (k2) for the reaction between AH- and HOONO, k2 = 236 +/- 14 M-1 s-1. Ascorbate displays higher selectivity for HOONO* than does methionine or 2-keto-4-thiomethylbutanoic acid, two substrates whose reactivity toward HOONO and HOONO* has previously been reported. The biological relevance of the reaction of ascorbate with peroxynitrite is discussed in terms of the rate constants and the concentrations of AH- typically found in biological systems; ascorbate may react with HOONO*, although the reaction with ground-state HOONO probably is too slow to occur in vivo.