Kelder P P, de Mol N J, Janssen L H
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Utrecht University, The Netherlands.
Biochem Pharmacol. 1991 Sep 27;42(8):1551-9. doi: 10.1016/0006-2952(91)90424-4.
Mechanistic aspects of the reaction of hydrogen peroxide with methemoglobin with respect to phenothiazine oxidation have been studied. Three phenothiazines, methoxy- (MoPZ), chlor- (CPZ) and methoxycarbonylpromazine (MaPZ), have been used. These phenothiazines differ only in substitution at the 2-position, which contributes substantially to the electron-donating properties of these compounds. Reaction with hydrogen peroxide oxidizes methemoglobin to ferrylhemoglobin, which contains iron(IV)-oxo porphyrin moiety and a protein radical. The phenothiazines are oxidized by ferrylhemoglobin in the presence of H2O2 mainly to their sulfoxides, with a radical cation as intermediate. The conversion rates (MoPZ greater than CPZ greater than MaPZ) decrease with the electron-withdrawing ability of the 2-substituent, as indicated by Hammett sigma para values. Hydrogen peroxide consumption during the reaction is similar for the three phenothiazines. Denaturation reactions that occur upon exposure of methemoglobin to hydrogen peroxide have been investigated. For this heme-protein cross-linking was studied by means of heme retention by the protein after methyl ethyl ketone extraction. Furthermore, oxygen consumption during the reaction was assayed, which indicates formation of protein-peroxy radicals. The extent of both heme-protein cross-linking and oxygen consumption is decreased by phenothiazines in the same order as the phenothiazine conversion rate. CPZ sulfoxide is not converted by methemoglobin in the presence of hydrogen peroxide, and CPZ sulfoxide shows no effect on heme-protein cross-linking and oxygen consumption. The results are explained by electron transfer from phenothiazine to the protein radical. Stronger electron donors (MoPZ greater than CPZ greater than MaPZ) are converted faster and by reducing the protein radical they better protect hemoglobin against denaturation. A catalytic cycle, that takes into account our observation and the existing knowledge of hemoglobin oxidation states, is presented.
关于吩噻嗪氧化，已研究了过氧化氢与高铁血红蛋白反应的机理。使用了三种吩噻嗪，即甲氧基 - （MoPZ）、氯 - （CPZ）和甲氧基羰基丙嗪（MaPZ）。这些吩噻嗪仅在2位的取代基不同，这对这些化合物的供电子性质有很大贡献。与过氧化氢反应会将高铁血红蛋白氧化为高铁血红素血红蛋白，其含有铁（IV） - 氧代卟啉部分和一个蛋白质自由基。在H2O2存在下，吩噻嗪主要被高铁血红素血红蛋白氧化为其亚砜，以自由基阳离子作为中间体。如哈米特σ对位值所示，转化率（MoPZ大于CPZ大于MaPZ）随着2 - 取代基的吸电子能力而降低。三种吩噻嗪在反应过程中的过氧化氢消耗量相似。已研究了高铁血红蛋白暴露于过氧化氢时发生的变性反应。为此，通过甲基乙基酮萃取后蛋白质对血红素的保留来研究血红素 - 蛋白质交联。此外，测定了反应过程中的氧气消耗量，这表明形成了蛋白质 - 过氧自由基。吩噻嗪以与吩噻嗪转化率相同的顺序降低血红素 - 蛋白质交联和氧气消耗的程度。在过氧化氢存在下，CPZ亚砜不会被高铁血红蛋白转化，并且CPZ亚砜对血红素 - 蛋白质交联和氧气消耗没有影响。结果通过从吩噻嗪到蛋白质自由基的电子转移来解释。更强的电子供体（MoPZ大于CPZ大于MaPZ）转化得更快，并且通过还原蛋白质自由基，它们能更好地保护血红蛋白免于变性。提出了一个催化循环，该循环考虑了我们的观察结果和血红蛋白氧化态的现有知识。
