Reaction of vitamin E compounds with N-nitrosated tryptophan derivatives and its analytical use.
We recently showed that nitrosated tryptophan residues may act as endogenous nitric oxide storage compounds. Here, a novel reaction of nitrosotryptophan derivatives is described, in the form of the release of nitric oxide from N-nitrosotryptophan derivatives initiated either by alpha-tocopherol or by its water-soluble form trolox. Alpha-tocopherol and trolox were found to release stoichiometric amounts of nitric oxide from N-acetyl-N-nitrosotryptophan as well as from the nitrosotryptophan residue in albumin. The reaction proceeds both in water and in lipophilic solution and reconstitutes the indole moiety of the tryptophan molecule quantitatively. During this reaction, alpha-tocopherol- and trolox-derived phenoxyl-type radicals were identified as intermediates by ESR spectrometry. The chemical mechanism of the NO-releasing process was established. Since S-nitrosothiols do not react under the applied conditions, it is suggested that the trolox-dependent release of nitric oxide may be utilizable for the detection of N-nitrosotryptophan residues in biological samples. Furthermore, as N-nitrosotryptophan derivatives do not undergo spontaneous decay in lipophilic environments, vitamin E may have the so far unrecognized function of preventing the accumulation of N-nitrosotryptophan residues to toxic concentrations in biological systems.
Müller
Karsten
K
Institut für Physiologische Chemie, Universitätsklinikum Essen, Hufelandstrasse 55, 45122 Essen, Germany.
Korth
Hans-Gert
HG
de Groot
Herbert
H
Kirsch
Michael
M
D000418:Albumins / Q000737:chemistry; D002839:Chromans / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D009569:Nitric Oxide / Q000737:chemistry; D009603:Nitroso Compounds / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000737:chemistry*; D014810:Vitamin E / Q000737:chemistry*
D000418:Albumins; D002839:Chromans; D009603:Nitroso Compounds; D011506:Proteins; D013438:Sulfhydryl Compounds; D014810:Vitamin E; D009569:Nitric Oxide; D014364:Tryptophan; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid