title: Methionine oxidation by peroxymonocarbonate, a reactive oxygen species formed from CO2/bicarbonate and hydrogen peroxide.
abstract: 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.
authors.affiliation: Center for Catalysis, Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA. der@chem.ufl.edu
authors.forename: David E
authors.initials: DE
authors.lastname: Richardson
authors.forename: Celeste A S
authors.initials: CA
authors.lastname: Regino
authors.forename: Huirong
authors.initials: H
authors.lastname: Yao
authors.forename: Jodie V
authors.initials: JV
authors.lastname: Johnson
mesh_terms: D000595:Amino Acid Sequence; D001639:Bicarbonates / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007700:Kinetics; D008715:Methionine / Q000737:chemistry*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet; D000515:alpha 1-Antitrypsin / Q000737:chemistry
chemical_list: D001639:Bicarbonates; D017382:Reactive Oxygen Species; D000515:alpha 1-Antitrypsin; D002245:Carbon Dioxide; D008715:Methionine; D006861:Hydrogen Peroxide