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GC-MS Studies on Nitric Oxide Autoxidation and IS/I-Nitrosothiol Hydrolysis to Nitrite in pH-Neutral Aqueous Buffers: Definite Results Using [sup.15]N and [sup.18]O Isotopes

Molecules (Basel, Switzerland), 2023-05, Vol.28 (11) [Peer Reviewed Journal]

COPYRIGHT 2023 MDPI AG ;ISSN: 1420-3049 ;EISSN: 1420-3049 ;DOI: 10.3390/molecules28114281

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  • Title:
    GC-MS Studies on Nitric Oxide Autoxidation and IS/I-Nitrosothiol Hydrolysis to Nitrite in pH-Neutral Aqueous Buffers: Definite Results Using [sup.15]N and [sup.18]O Isotopes
  • Author: Tsikas, Dimitrios
  • Subjects: Hydrolysis ; Nitrogen oxide
  • Is Part Of: Molecules (Basel, Switzerland), 2023-05, Vol.28 (11)
  • Description: Nitrite (O=N-O[sup.−], NO[sub.2] [sup.−]) and nitrate (O=N(O)-O[sup.−], NO[sub.3] [sup.−]) are ubiquitous in nature. In aerated aqueous solutions, nitrite is considered the major autoxidation product of nitric oxide ([sup.●]NO). [sup.●]NO is an environmental gas but is also endogenously produced from the amino acid L-arginine by the catalytic action of [sup.●]NO synthases. It is considered that the autoxidation of [sup.●]NO in aqueous solutions and in O[sub.2]-containing gas phase proceeds via different neutral (e.g., O=N-O-N=O) and radical (e.g., ONOO[sup.●]) intermediates. In aqueous buffers, endogenous S-nitrosothiols (thionitrites, RSNO) from thiols (RSH) such as L-cysteine (i.e., S-nitroso-L-cysteine, CysSNO) and cysteine-containing peptides such as glutathione (GSH) (i.e., S-nitrosoglutathione, GSNO) may be formed during the autoxidation of [sup.●]NO in the presence of thiols and dioxygen (e.g., GSH + O=N-O-N=O → GSNO + O=N-O[sup.−] + H[sup.+]; pK[sub.a] [sup.HONO], 3.24). The reaction products of thionitrites in aerated aqueous solutions may be different from those of [sup.●]NO. This work describes in vitro GC-MS studies on the reactions of unlabeled ([sup.14]NO[sub.2] [sup.−]) and labeled nitrite ([sup.15]NO[sub.2] [sup.−]) and RSNO (RS[sup.15]NO, RS[sup.15]N[sup.18]O) performed in pH-neutral aqueous buffers of phosphate or tris(hydroxyethylamine) prepared in unlabeled (H[sub.2] [sup.16]O) or labeled H[sub.2]O (H[sub.2] [sup.18]O). Unlabeled and stable-isotope-labeled nitrite and nitrate species were measured by gas chromatography-mass spectrometry (GC-MS) after derivatization with pentafluorobenzyl bromide and negative-ion chemical ionization. The study provides strong indication for the formation of O=N-O-N=O as an intermediate of [sup.●]NO autoxidation in pH-neutral aqueous buffers. In high molar excess, HgCl[sub.2] accelerates and increases RSNO hydrolysis to nitrite, thereby incorporating [sup.18]O from H[sub.2] [sup.18]O into the SNO group. In aqueous buffers prepared in H[sub.2] [sup.18]O, synthetic peroxynitrite (ONOO[sup.−]) decomposes to nitrite without [sup.18]O incorporation, indicating water-independent decomposition of peroxynitrite to nitrite. Use of RS[sup.15]NO and H[sub.2] [sup.18]O in combination with GC-MS allows generation of definite results and elucidation of reaction mechanisms of oxidation of [sup.●]NO and hydrolysis of RSNO.
  • Publisher: MDPI AG
  • Language: English
  • Identifier: ISSN: 1420-3049
    EISSN: 1420-3049
    DOI: 10.3390/molecules28114281
  • Source: Geneva Foundation Free Medical Journals at publisher websites
    PubMed Central
    Directory of Open Access Journals
    Alma/SFX Local Collection
    ProQuest Central
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