SNitrosothiols

Snitrosothiols, collectively referred to as RSNOs, are organic compounds in which a nitroso group is bound to a thiol sulfur atom (R-S-NO). They are formed when thiols react with nitrosating agents and are recognized as endogenous reservoirs and carriers of nitric oxide (NO) that participate in signaling through NO release and S-nitrosylation of proteins.

Structure and chemistry: The RSNO group features a sulfur-nitroso linkage that can be cleaved under certain conditions. RSNOs are generally stable under controlled conditions but are sensitive to light, heat, trace metals, and reducing environments. They can release NO through homolytic or heterolytic pathways, and can transfer the nitroso group to other thiols in transnitrosation reactions, forming new RSNOs and reshuffling nitrosothiol pools.

Biosynthesis and biological relevance: In biological systems, RSNOs form by nitrosation of thiols with nitrosating species such as nitrous acid or nitrosating enzymes and reactive nitrogen species generated during nitric oxide metabolism. Glutathione S-nitrosothiol (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) are common examples. RSNOs function as NO donors and as mediators of protein S-nitrosylation, influencing vascular tone, signaling pathways, and cytoprotective responses.

Detection, synthesis, and applications: In laboratory settings, RSNOs are synthesized by nitrosating thiols with nitrosating agents and can be detected by UV-Vis spectroscopy, electrochemical methods, or chemiluminescent measurement of released NO. In research and, to a limited extent, therapeutic contexts, RSNO donors are used to study NO biology and as potential NO-delivery agents.