Herold Susanna, Boccini Francesca
Laboratorium für Anorganische Chemie, Eidgenössische Technische Hochschule, ETH Hönggerberg, CH-8093 Zürich, Switzerland.
Inorg Chem. 2006 Aug 21;45(17):6933-43. doi: 10.1021/ic060469g.
In this work, we showed that the reaction of peroxynitrite with MbFe(II)NO, in analogy to the corresponding reaction with HbFe(II)NO (Herold, S. Inorg. Chem. 2004, 43, 3783-3785), proceeds in two steps via the formation of MbFe(III)NO, from which NO* dissociates to produce iron(III)myoglobin (Mb = myoglobin; Hb = hemoglobin). The second-order rate constants for the first steps are on the order of 10(4) and 10(3) M(-1) s(-1), for the reaction of peroxynitrite with MbFe(II)NO and HbFe(II)NO, respectively. For both proteins, we found that the values of the second-order rate constants increase with decreasing pH, an observation that suggests that HOONO is the species responsible for oxidation of the iron center. Nevertheless, it cannot be excluded that the pH-dependence arises from different conformations taken up by the proteins at different pH values. In the presence of 1.2 mM CO2, the values of the second-order rate constants are larger, on the order of 10(5) and 10(4) M(-1) s(-1), for the reaction of peroxynitrite with MbFe(II)NO and HbFe(II)NO, respectively. The pH-dependence of the values for the reaction with MbFe(II)NO suggests that ONOOCO2- or the radicals produced from its decay (CO3*-/NO2*) are responsible for the oxidation of MbFe(II)NO to MbFe(III)NO. In the presence of large amounts of nitrite (in the tens and hundreds of millimoles range), we observed a slight acceleration of the rate of oxidation of HbFe(II)NO by peroxynitrite. A catalytic rate constant of 40 +/- 2 M(-1) s(-1) was determined at pH 7.0. Preliminary studies of the reaction between nitrite and HbFe(II)NO showed that this compound also can oxidize the iron center, albeit at a significantly slower rate. At pH 7.0, we obtained an approximate second-order rate constant of 3 x 10(-3) M(-1) s(-1).
在本研究中，我们发现，过氧亚硝酸盐与肌红蛋白亚铁-亚硝酰配合物（MbFe(II)NO）的反应，类似于其与血红蛋白亚铁-亚硝酰配合物（HbFe(II)NO）的相应反应（Herold, S. Inorg. Chem. 2004, 43, 3783 - 3785），分两步进行，先形成肌红蛋白高铁-亚硝酰配合物（MbFe(III)NO），然后NO解离生成高铁肌红蛋白（Mb = 肌红蛋白；Hb = 血红蛋白）。第一步反应的二级速率常数分别约为10(4)和10(3) M(-1) s(-1)，分别对应过氧亚硝酸盐与MbFe(II)NO和HbFe(II)NO的反应。对于这两种蛋白质，我们发现二级速率常数的值随pH降低而增加——这一观察结果表明，HOONO是负责铁中心氧化的物种。然而，不能排除pH依赖性是由蛋白质在不同pH值下采取的不同构象引起的。在存在1.2 mM CO2的情况下，二级速率常数的值更大，分别约为10(5)和10(4) M(-1) s(-1)，分别对应过氧亚硝酸盐与MbFe(II)NO和HbFe(II)NO的反应。与MbFe(II)NO反应的值的pH依赖性表明，ONOOCO2-或其分解产生的自由基（CO3-/NO2*）是将MbFe(II)NO氧化为MbFe(III)NO的原因。在存在大量亚硝酸盐（数十至数百毫摩尔范围内）的情况下，我们观察到过氧亚硝酸盐氧化HbFe(II)NO的速率略有加快。在pH 7.0时测定的催化速率常数为40 +/- 2 M(-1) s(-1)。亚硝酸盐与HbFe(II)NO之间反应的初步研究表明，该化合物也能氧化铁中心，尽管速率明显较慢。在pH 7.0时，我们得到的近似二级速率常数为3 x 10(-3) M(-1) s(-1)。
