Lymar S V, Jiang Q, Hurst J K
Department of Chemistry, Washington State University, Pullman 99163-4630, USA.
Biochemistry. 1996 Jun 18;35(24):7855-61. doi: 10.1021/bi960331h.
Peroxynitrite ion (ONO2-) reacted rapidly with CO2 to form a short-lived intermediate provisionally identified as the ONO2CO2- adduct. This adduct was more reactive in tyrosine oxidation than ONO2- itself and produced 3-nitrotyrosine and 3,3'-dityrosine as the major oxidation products. With tyrosine in excess, the rate of 3-nitrotyrosine formation was independent of the tyrosine concentration and was determined by the rate of formation of the ONO2CO2- adduct. The overall yield of oxidation products was also independent of the concentration of tyrosine and medium acidity; approximately 19% of the added ONO2- was converted to products under all reaction conditions. However, the 3-nitrotyrosine/3,3'-dityrosine product ratio depended upon the pH, tyrosine concentration, and absolute reaction rate. These data are in quantitative agreement with a reaction mechanism in which the one-electron oxidation of tyrosine by ONO2CO2- generates tyrosyl and NO2 radicals as intermediary species, but are inconsistent with mechanisms that invoke direct electrophilic attack on the tyrosine aromatic ring by the adduct. Based upon its reactivity characteristics, ONO2CO2- has a lifetime shorter than 3 ms and a redox potential in excess of 1 V, and oxidizes tyrosine with a bimolecular rate constant greater than 2 x 10(5) M-1 s-1. In comparison, in CO2-free solutions, oxidation of tyrosine by peroxynitrite was much slower and gave significantly lower yields (approximately 8%) of the same products. When tyrosine was the limiting reactant, 3,5-dinitrotyrosine was found among the reaction products of the CO2-catalyzed reaction, but this compound was not detected in the uncatalyzed reaction.
过氧亚硝酸根离子（ONO2-）与二氧化碳迅速反应，形成一种寿命短暂的中间体，暂定为ONO2CO2-加合物。该加合物在酪氨酸氧化反应中比ONO2-本身更具反应活性，并产生3-硝基酪氨酸和3,3'-二酪氨酸作为主要氧化产物。当酪氨酸过量时，3-硝基酪氨酸的形成速率与酪氨酸浓度无关，而是由ONO2CO2-加合物的形成速率决定。氧化产物的总产率也与酪氨酸浓度和介质酸度无关；在所有反应条件下，约19%的添加ONO2-转化为产物。然而，3-硝基酪氨酸/3,3'-二酪氨酸产物比例取决于pH值、酪氨酸浓度和绝对反应速率。这些数据与一种反应机制在定量上相符，即ONO2CO2-对酪氨酸的单电子氧化产生酪氨酰基和NO2自由基作为中间物种，但与加合物直接对酪氨酸芳香环进行亲电攻击的机制不一致。基于其反应活性特征，ONO2CO2-的寿命短于3毫秒，氧化还原电位超过1伏，以大于2×10(5) M-1 s-1的双分子速率常数氧化酪氨酸。相比之下，在无二氧化碳的溶液中，过氧亚硝酸根对酪氨酸的氧化要慢得多，相同产物的产率也显著较低（约8%）。当酪氨酸是限量反应物时，在二氧化碳催化反应的产物中发现了3,5-二硝基酪氨酸，但在未催化反应中未检测到该化合物。
