Peroxynitrite does not decompose to singlet oxygen ((1)Delta (g)O(2)) andnitroxyl (NO(-)).
According to Khan et al. [Khan, A. U., Kovacic, D., Kolbanovskiy, A., Desai, M., Frenkel, K. & Geacintov, N. E. (2000) Proc. Natl. Acad. Sci. USA 97, 2984-2989], peroxynitrite (ONOO(-)) decomposes after protonation to singlet oxygen ((1)Delta(g)O(2)) and singlet oxonitrate (nitroxyl, (1)NO(-)) in high yield. They claimed to have observed nitrosyl hemoglobin from the reaction of NO(-) with methemoglobin; however, contamination with hydrogen peroxide gave rise to ferryl hemoglobin, the spectrum of which was mistakenly assigned to nitrosyl hemoglobin. We have carried out UV-visible and EPR experiments with methemoglobin and hydrogen peroxide-free peroxynitrite and find that no NO(-) is formed. With this peroxynitrite preparation, no light emission from singlet oxygen at 1270 nm is observed, nor is singlet oxygen chemically trapped; however, singlet oxygen was trapped when hydrogen peroxide was also present, as previously described [Di Mascio, P., Bechara, E. J. H., Medeiros, M. H. G., Briviba, K. & Sies, H. (1994) FEBS Lett. 355, 287-289]. Quantum mechanical and thermodynamic calculations show that formation of the postulated intermediate, a cyclic form of peroxynitrous acid (trioxazetidine), and the products (1)NO(-) and (1)Delta(g)O(2) requires Gibbs energies of ca. +415 kJ .mol(-1) and ca. +180 kJ.mol(-1), respectively. Our results show that the results of Khan et al. are best explained by interference from contaminating hydrogen peroxide left from the synthesis of peroxynitrite.
Martinez
G R
GR
Departamento de Bioquimica, Instituto de Quimica, Universidade de São Paulo, CP 26077, CEP 05513-970, São Paulo, SP, Brazil.
Di Mascio
P
P
Bonini
M G
MG
Augusto
O
O
Briviba
K
K
Sies
H
H
Maurer
P
P
Röthlisberger
U
U
Herold
S
S
Koppenol
W H
WH
D002851:Chromatography, High Pressure Liquid; D013058:Mass Spectrometry; D009566:Nitrates / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry*; D010100:Oxygen; D026082:Singlet Oxygen
D009566:Nitrates; D009589:Nitrogen Oxides; D026082:Singlet Oxygen; C039642:peroxynitric acid; C039900:nitroxyl; D010100:Oxygen