New features of the NO/H2S crosstalk: a chemical basis

BARI, SARA E.; OLABE, JOSÉ A.

Gasotransmitters in Plants The Rise of a New Paradigm in Cell Signaling

Springer

Año: 2016; p. 289 - 327

Theanalysis of the NO + H2S reaction revealed the formation of nitroxyl(HNO), a crucial intermediate with specific signaling abilities as compared toNO. A comparison of the H2S reactivity with other biologicallyrelevant reductants such as ascorbate, hydroquinone, phenols and thiolatesassists the mechanistic study. We also discuss the specificity of the reversible transnitrosationreactions using HS− instead of thiolates RSH, highlighting the roleof thionitrous acid HSNO, disulfide HS2−, polysulfides HSx?and nitrosodisulfide NOS2− anions in putative proteinmodifications. Controversial characterization and reactivity issues associatedwith the latter species, either as free or eventually as bound ligands atiron-binding sites are presented and discussed. The nitroprusside ion and thedinitrosyl iron complexes (DNIC) have been chosen as examples of rich non-hemereactivity for HS−, and diverse heme-models and selected enzymesallowed discussing the new possibilities for the NO/H2S crosstalkemerging upon coordination. A specific focus has been directed to how HS− mightreact with NO2−, related to the non-enzymatic productionof NO in the vasculature under anoxia and high concentrations of HS−,as well as other metabolic routes of NO2− promoted byiron-heme binding. An insight into the reactivity of HS− towardperoxynitrite also connects with the chemistry of other systems associated withthe production of sulfenic species as intermediates. Overall, the chapterhighlights the role of sulfur-based S·−, S2·−and hybrid N-S radicals for adequately disclosing the mechanistic issues, bothin anaerobic and aerobic conditions, and also provides a discussion onaccessible associative routes for HS? and NO/NOx reactantsin order to surmount the high activation barriers predicted by unfavorableredox potentials.