Chemical mechanisms underlying the vasodilator and platelet anti-aggregating properties of S-nitroso-N-acetyl-DL-penicillamine and S-nitrosoglutathione.

The chemistries of S-nitroso-DL-penicillamine (SNAP) and S-nitrosoglutathione (GSNO) in relation to their ability to relax vascular smooth muscle and prevent platelet aggregation have been investigated. Metal ion catalysis greatly accelerates the decomposition of SNAP, but has little effect on GSNO. Instead, NO release from GSNO is effected either by NO transfer to a free thiol (e.g. cysteine), or by enzymatic cleavage of the glutamyl-cystyl peptide bond. In both cases the resulting nitrosothiol (i.e. S-nitrosocysteine and S-nitrosocystylglycine, respectively) is susceptible to metal ion catalysed NO release. We conclude that transnitrosation or enzymatic cleavage are obligatory steps in the mechanism of NO release from GSNO, whereas SNAP needs only the presence of metal ions to effect this process. The different modes of NO production may go some way towards explaining the different physiological effectiveness of these S-nitrosothiols as vasodilators and inhibitors of platelet aggregation.