The kinetics of the reaction of nitrogen dioxide with iron(II)- and iron(III) cytochrome c.
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 °C. NO2 oxidizes N-acetyltyrosine amide and N-acetyltryptophan amide with rate constants of (3.1±0.3)×10(5) and (1.1±0.1)×10(6) M(-1) s(-1), 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±0.7)×10(6) M(-1) s(-1) at pH 7.2. NO2 oxidizes iron(II)cytochrome c with a second-order rate constant of (6.6±0.5)×10(7) M(-1) s(-1) 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-most probably via reaction at the solvent-accessible heme edge-whereas 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.
Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland. Electronic address: domazou@inorg.chem.ethz.ch.
Anastasia S
AS
Domazou
Institute of Applied Radiation Chemistry, Faculty of Chemistry, Lodz University of Technology, 93-590 Lodz, Poland.
Lidia
L
Gebicka
Institute of Applied Radiation Chemistry, Faculty of Chemistry, Lodz University of Technology, 93-590 Lodz, Poland.
Joanna
J
Didik
Institute of Applied Radiation Chemistry, Faculty of Chemistry, Lodz University of Technology, 93-590 Lodz, Poland.
Jerzy L
JL
Gebicki
Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland.
Benjamin
B
van der Meijden
Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich CH-8093, Switzerland.
Willem H
WH
Koppenol
D000596:Amino Acids / Q000737:chemistry; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism*; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D009585:Nitrogen Dioxide / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D011675:Pulse Radiolysis; D014364:Tryptophan / Q000031:analogs & derivatives / Q000737:chemistry; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry
D000596:Amino Acids; C019142:N-acetyltyrosylamide; C016952:N-acetyltryptophanamide; D014443:Tyrosine; D006418:Heme; D014364:Tryptophan; D045304:Cytochromes c; D007501:Iron; D009585:Nitrogen Dioxide
Amino acid radical; CO(2); Cytochrome c; Free radicals; Kinetics; N-acetyltryptophan amide; N-acetyltyrosine amide; NO(2)(); Peroxynitrite; Protein radical; Pulse radiolysis; Rate constant; Tryptophan radical; Tyrosine radical