Methionine oxidation by peroxymonocarbonate, a reactive oxygen species formed from CO2/bicarbonate and hydrogen peroxide

Free Radic Biol Med. 2003 Dec 15;35(12):1538-50. doi: 10.1016/j.freeradbiomed.2003.08.019.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bicarbonates / chemistry*
  • Carbon Dioxide / chemistry*
  • Chromatography, High Pressure Liquid
  • Hydrogen Peroxide / chemistry*
  • Kinetics
  • Methionine / chemistry*
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Reactive Oxygen Species / chemistry*
  • Spectrometry, Mass, Electrospray Ionization
  • Spectrophotometry, Ultraviolet
  • alpha 1-Antitrypsin / chemistry


  • Bicarbonates
  • Reactive Oxygen Species
  • alpha 1-Antitrypsin
  • Carbon Dioxide
  • Methionine
  • Hydrogen Peroxide