Snitrosothiol

Snitrosothiol, or S-nitrosothiol (RSNO), refers to organic compounds containing the functional group S–NO bound to a thiol (R–S–NO). They can form by nitrosation of thiols and function as reservoirs and donors of nitric oxide (NO) in biological systems. Prototypical examples include S-nitrosoglutathione (GSNO) and S-nitrosocysteine (CysNO). RSNOs are involved in NO signaling and nitrosative chemistry, with cellular levels regulated by enzymes such as GSNO reductase (GSNOR).

Formation and reactivity: RSNOs form when thiols are nitrosated by nitrosating agents such as nitrous acid (HONO) or nitrosonium (NO+). In biology, NO-derived species and metal ions can mediate nitrosation, or preformed RSNOs can transfer the NO group to other thiols in transnitrosation reactions. They can also arise from reactions of NO with thiyl radicals.

Stability and decomposition: RSNOs are relatively labile; they can decompose thermally or photochemically to give NO and the corresponding thiol, or transfer the NO group to other thiols. Metal ions, enzymes, pH, and reducing conditions influence their persistence. As NO donors, they participate in signaling through transnitrosation and direct NO release.

Biological roles: GSNO and CysNO are widely studied. RSNOs contribute to vasodilation, platelet function, and neurotransmission, and participate in nitrosative signaling networks. Cellular systems regulate their levels (for example via GSNO reductase) to balance nitrosation and denitrosation.

Analytical aspects: Detecting RSNOs in biological samples is challenging due to lability and interferences. Common approaches include chemiluminescent and spectroscopic methods, as well as trapping or derivatization techniques; interpretation requires care.