Selenol Nitrosation and Se-Nitrososelenol Homolysis: A Reaction Path with Possible Biochemical Implications

The biological role of nitric oxide (NO) as a secondary messenger, for instance in the cardiovascular system, has been known for more tha residues of oxyhemoglobin leading to S-nitrosothiol functions (RSNO) supports the active transport of NO, which can be liberated enzymatically from RSNO. Accordingly, S-nitrosothiols are efficient vasodilators, as is NO, but also intrinsically toxic.[1–3] Se-nitrososelenols (RSeNO) are unknown; however, there may be factors common to the biological cycles of NO and those of selenoproteins.[4] For example, selenoproteins are efficient reagents for peroxynitrite reduction, [5] and S-nitrosothiols can be substrates of mammalian selenoenzymes such as GPx (glutathione peroxidases) and TrxR (thioredoxin reductases).[6–10] Whether the selenocysteine moieties (Sec) in the active centers of TrxR and GPx play a particular role in the course of the enzymatic NO liberation from S-nitrosothiols is still unknown. Wang et al. proposed recently that in course of the in vitro cleavage of Snitrosoglutathione (GSNO), catalyzed by GPx or by bis(4-chlorophenyl)diselenide, selenols could play a crucial role.[10] In our opinion the key steps of this kind of catalysis may be selenol nitrosation with subsequent Se-nitrososelenol homolysis, a yet-unknown type of reaction in selenoprotein chemistry. To test this hypothesis, we studied model reactions for the nitrosation of various selenols and thiols. n a decade. Nitrosation of the cysteine