The kinetics of the reaction of nitrogen dioxide with iron(II)- and iron(III) cytochrome c

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• 作者：Anastasia S. Domazou^a ; ^{domazou@inorg.chem.ethz.ch" class="auth_mail} ; Lidia Gebicka^b ; Joanna Didik^b ; Jerzy L. Gebicki^b ; Benjamin van der Meijden^a ; ¹ ; Willem H. Koppenol^a
• 关键词：a ; trivial terms (in italic) and systematic names for the compounds used in this work are AA amino acid radical ; ABTS ; 2 ; 2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) diammonium salt ; ABTS2&minus ; 2 ; 2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) ; ABTS&minus ; radical of 2 ; 2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) ; Br2&minus ; bromine radical ; dibromide (1&minus ; ) ; CO2 ; carbon dioxide ; dioxidocarbon ; CO2&minus ; formyl radical anion ; dioxidocarbonate (1&minus ; ) ; CO3&minus ; carbonate ra
• 刊名：Free Radical Biology and Medicine
• 出版年：April, 2014
• 年：2014
• 卷：69
• 期：Complete
• 页码：172-180
• 全文大小：601 K

文摘

The reactions of NO₂ with both oxidized and reduced cytochrome c at pH 7.2 and 7.4, respectively, and with N-acetyltyrosine amide and N-acetyltryptophan amide at pH 7.3 were studied by pulse radiolysis at 23 掳C. NO₂ oxidizes N-acetyltyrosine amide and N-acetyltryptophan amide with rate constants of (3.1卤0.3)脳10⁵ and (1.1卤0.1)脳10⁶ M^鈭? s^鈭?, respectively. With iron(III)cytochrome c, the reaction involves only its amino acids, because no changes in the visible spectrum of cytochrome c are observed. The second-order rate constant is (5.8卤0.7)脳10⁶ M^鈭? s^鈭? at pH 7.2. NO₂ oxidizes iron(II)cytochrome c with a second-order rate constant of (6.6卤0.5)脳10⁷ M^鈭? s^鈭? at pH 7.4; formation of iron(III)cytochrome c is quantitative. Based on these rate constants, we propose that the reaction with iron(II)cytochrome c proceeds via a mechanism in which 90% of NO₂ oxidizes the iron center directly鈥攎ost probably via reaction at the solvent-accessible heme edge鈥攚hereas 10% oxidizes the amino acid residues to the corresponding radicals, which, in turn, oxidize iron(II). Iron(II)cytochrome c is also oxidized by peroxynitrite in the presence of CO₂ to iron(III)cytochrome c, with a yield of ~60% relative to peroxynitrite. Our results indicate that, in vivo, NO₂ will attack preferentially the reduced form of cytochrome c; protein damage is expected to be marginal, the consequence of formation of amino acid radicals on iron(III)cytochrome c.