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Abstract
Tryptophan and melatonin are nitrated by peroxynitrite; tryptophan residues in proteins are susceptible to attack by reactive nitrogen species. Nitrated tryptophan might therefore be used as a biomarker for the involvement of reactive species derived from nitrogen oxide in a variety of pathophysiological conditions. The radical character of the tryptophan (Trp) and N-acetyl-l-tryptophan (N-AcTrp) nitration with peroxynitrite is shown using 15N-CIDNP. During the decay of peroxynitrite-15N in the presence of Trp at pH 5 in the probe of a 15N-NMR spectrometer, the 15N-NMR signals of various nitrated tryptophans (15NO2-Trp) show emission (E). The effects are built up in radical pairs [Trp√, 15]F formed by diffusive encounters of radicals 15
and Trp√ generated during decay of peroxynitrite-15N in the presence of Trp. Similar 15N-CIDNP effects are observed during reaction of Trp and/or N-AcTrp using the nitrating systems H15NO3, H15NO4 and H2O2/15
/HRP, which are also built up in radical pairs [Trp√, 15
]F. During nitration of melatonin (Mel) with peroxynitrite-15N and H15NO4, the 15N-NMR signal of 4-nitromelatonin (4-15NO2-Mel) shows emission arising from radical pairs [Mel√, 15
]F which are formed in an analogous manner.
| Abbreviations | ||
| 1 | = | 3-methylindane |
| 2 | = | 3-methyl-5-methoxyindane |
| A | = | enhanced absorption |
| AcOH | = | acetic acid |
| c | = | cage product |
| CIDNP | = | chemically induced dynamic nuclear polarization |
| E | = | emission |
| e | = | escape product |
| F | = | radical precursor |
| g | = | g value |
| HRP | = | horseradish peroxidase |
| Mel | = | melatonin (N-[2-(5-methoxy-1H-indol-3yl)ethyl]-acetamide |
| MetMb | = | Metmyoglobin |
| MPO | = | myeloperoxidase |
| N | = | no CIDNP effect |
| N-AcTrp | = | N-acetyl-l-tryptophan |
| N-AcTrp-NH2 | = | N-acetyl-l-tryptophan amide |
| NO2-Mel | = | nitromelatonin |
| NO2-N-AcTrp | = | nitro-N-acetyl-l-tryptophan |
| NO2-Trp | = | nitrotryptophan |
| NO2-Tyr | = | nitrotyrosine |
| RNS | = | reactive nitrogen species |
| S | = | singlet state |
| Abbreviations | ||
| 1 | = | 3-methylindane |
| 2 | = | 3-methyl-5-methoxyindane |
| A | = | enhanced absorption |
| AcOH | = | acetic acid |
| c | = | cage product |
| CIDNP | = | chemically induced dynamic nuclear polarization |
| E | = | emission |
| e | = | escape product |
| F | = | radical precursor |
| g | = | g value |
| HRP | = | horseradish peroxidase |
| Mel | = | melatonin (N-[2-(5-methoxy-1H-indol-3yl)ethyl]-acetamide |
| MetMb | = | Metmyoglobin |
| MPO | = | myeloperoxidase |
| N | = | no CIDNP effect |
| N-AcTrp | = | N-acetyl-l-tryptophan |
| N-AcTrp-NH2 | = | N-acetyl-l-tryptophan amide |
| NO2-Mel | = | nitromelatonin |
| NO2-N-AcTrp | = | nitro-N-acetyl-l-tryptophan |
| NO2-Trp | = | nitrotryptophan |
| NO2-Tyr | = | nitrotyrosine |
| RNS | = | reactive nitrogen species |
| S | = | singlet state |