Peroxynitrite-induced nitration of tyrosine-34 does not inhibit Escherichia coli iron superoxide dismutase.
The peroxynitrite anion is a potent oxidizing agent, formed by the diffusion-limited combination of nitric oxide and superoxide, and its production under physiological conditions is associated with the pathologies of a number of inflammatory and neurodegenerative diseases. Nitration of Escherichia coli iron superoxide dismutase (Fe-SOD) by peroxynitrite was investigated, and demonstrated by spectral changes and electrospray mass spectroscopic analysis. HPLC and mass studies of the tryptic digests of the mono-nitrated Fe-SOD indicated that tyrosine-34 was the residue most susceptible to nitration by peroxynitrite. Exclusive nitration of this residue occurred when Fe-SOD was exposed to a cumulative dose of 0.4 mM peroxynitrite. Unlike with human Mn-SOD, this single modification did not inactivate E. coli Fe-SOD at pH 7.4. When Fe-SOD was exposed to higher concentrations of peroxynitrite (7 mM), eight tyrosine residues per subunit of the protein, of the nine available, were nitrated without loss of catalytic activity of the enzyme. The pK(a) of nitrated tyrosine-34 was determined to be 7.95+/-0.15, indicating that the peroxynitrite-modified enzyme appreciably maintains its protonation state under physiological conditions.
Soulère
L
L
Groupe de Chimie Organique Biologique, Laboratoire de Synthèse et Physico-Chimie de Molécules d'Intérêt Biologique, UMR 5068, Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse cedex 4, France.
Claparols
C
C
Périé
J
J
Hoffmann
P
P
D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000201:enzymology*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D030421:Peroxynitrous Acid / Q000494:pharmacology*; D011487:Protein Conformation; D021241:Spectrometry, Mass, Electrospray Ionization; D013482:Superoxide Dismutase / Q000737:chemistry / Q000378:metabolism*; D014443:Tyrosine
D007527:Isoenzymes; D010446:Peptide Fragments; D030421:Peroxynitrous Acid; D014443:Tyrosine; D013482:Superoxide Dismutase