How is Nitric Oxide (NO) Converted into Nitrosonium Cations (NO + ) in Living Organisms? (Based on the Results of Optica
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Applied Magnetic Resonance
ORIGINAL PAPER
How is Nitric Oxide (NO) Converted into Nitrosonium Cations (NO+) in Living Organisms? (Based on the Results of Optical and EPR Analyses of Dinitrosyl Iron Complexes with Thiol‑Containing Ligands) Anatoly F. Vanin1,2 Published online: 20 October 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The present work provides theoretical and experimental foundations for the ability of dinitrosyl iron complexes (DNICs) with thiol-containing ligands to be not only the donors of neutral NO molecules, but also the donors of nitrosonium cations (NO+) in living organisms ensuring S-nitrosation of various proteins and lowmolecular-weight compounds. It is proposed that the emergence of those cations in DNICs is related to disproportionation reaction of NO molecules, initiated by their binding with F e2+ ions (two NO molecules per one ion). At the same time, possible hydrolysis of iron-bound nitrosonium cations is prevented by the electron density transition to nitrosonium cations from sulfur atoms of thiol-containing ligands, which are included in the coordination sphere of iron. It allows supposing that iron in iron–nitrosyl complexes of DNICs has a d7 electronic configuration. This supposition is underpinned by experimental data revealing that a half of nitrosyl ligands are converted into S-nitrosothiols (RSNOs) when those complexes decompose, with the other half of those ligands released in the form of neutral NO molecules.
1 Part 1. Dinitrosyl Iron Complexes with Thiol‑Containing Ligands as Sources of Nitrosonium Cations. Theoretical Justification It is widely acknowledged that all living organisms, ranging from microorganisms and plants to animals and humans, continuously synthesize nitric oxide (NO), the simplest chemical compound, through enzymes. This compound is one of the main versatile regulators modulating various physiological and biochemical processes in * Anatoly F. Vanin [email protected] 1
Semenov Federal Research Center of Chemical Physics, Russian Academy of Sciences, Moscow, Russia
2
Institute for Regenerative Medicine, Sechenov University, Moscow, Russia
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living organisms [1–3]. The biological effect of NO originates from its ability to easily penetrate the cell membranes and get into cells without being mediated by cell receptors, with a subsequent binding with heme groups of various heme-containing proteins, such as guanylate cyclase, thus initiating activation or inhibition of those proteins. Biological activity of NO derivatives, nitrosonium cations (NO+), which occur in cells and tissues due to the one-electron oxidation of neutral NO molecules, is also important. In terms of biological effects, nitrosonium cations replace protons in thiol groups of various thiol-containing compounds, leading to the respective S-nitrosothiols (RS-NO) being formed. This modification of thiol groups in proteins significantly increases the reactivity of those groups, both in terms of their reactions
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