Richardson David E, Regino Celeste A S, Yao Huirong, Johnson Jodie V
Center for Catalysis, Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA.
Free Radic Biol Med. 2003 Dec 15;35(12):1538-50. doi: 10.1016/j.freeradbiomed.2003.08.019.
Kinetic and thermodynamic evidence is reported for the role of the peroxymonocarbonate ion, HCO4-, as a reactive oxygen species in biology. Peroxymonocarbonate results from the equilibrium reaction of hydrogen peroxide with bicarbonate via the perhydration of CO2. The kinetic parameters for HCO4- oxidation of free methionine have been obtained (k1 = 0.48 +/- 0.08 M(-1)s(-1) by a spectrophotometric initial rate method). At the physiological concentration of bicarbonate in blood ( approximately 25 mM), it is estimated that peroxymonocarbonate formed in equilibrium with hydrogen peroxide will oxidize methionine approximately 2-fold more rapidly than plasma H2O2 itself. As an example of methionine oxidation in proteins, the bicarbonate-catalyzed hydrogen peroxide oxidation of alpha1-proteinase inhibitor (alpha1-PI) has been investigated via its inhibitory effect on porcine pancreatic elastase activity. The second-order rate constant for HCO4- oxidation of alpha1-PI (0.36 +/- 0.06 M(-1)s(-1)) is comparable to that of free methionine, suggesting that methionine oxidation is occurring. Further evidence for methionine oxidation, specifically involving Met358 and Met351 of the alpha1-PI reactive center loop, has been obtained through amino acid analyses and mass spectroscopic analyses of proteolytic digests of the oxidized alpha1-PI. These results strongly suggest that HCO4- should be considered a reactive oxygen species in aerobic metabolism.
有动力学和热力学证据表明过一碳酸根离子（HCO4-）在生物学中作为一种活性氧发挥作用。过一碳酸根是由过氧化氢与碳酸氢根通过二氧化碳的水合作用发生平衡反应生成的。通过分光光度法初始速率法已获得了HCO4-氧化游离蛋氨酸的动力学参数（k1 = 0.48 +/- 0.08 M(-1)s(-1)）。在血液中碳酸氢根的生理浓度（约25 mM）下，据估计与过氧化氢处于平衡状态形成的过一碳酸根氧化蛋氨酸的速度比血浆中的H2O2本身快约2倍。作为蛋白质中蛋氨酸氧化的一个例子，通过其对猪胰弹性蛋白酶活性的抑制作用研究了碳酸氢根催化的过氧化氢对α1-蛋白酶抑制剂（α1-PI）的氧化。HCO4-氧化α1-PI的二级速率常数（0.36 +/- 0.06 M(-1)s(-1)）与游离蛋氨酸的相当，表明蛋氨酸发生了氧化。通过对氧化的α1-PI蛋白水解消化产物的氨基酸分析和质谱分析，获得了蛋氨酸氧化的进一步证据，特别是涉及α1-PI反应中心环的Met358和Met351。这些结果强烈表明HCO4-应被视为有氧代谢中的一种活性氧。
