The previous funding period examined the chemical basis for the interactions between thiols, peroxynitrite and nitric oxide. It has become apparent that S-nitrosothiols (RSNO), biological metabolites of nitric oxide and thiols, play divers roles in potentiating and modulating the effects of nitric oxide. These include an anti-platelet function and vessel relaxation in terms of extracellular effects, and is also the intracellular modulation of enzyme activities and signaling pathways. Very little is known about the metabolism of RSNO. It is often assumed that these compounds spontaneously liberate nitric oxide and these compounds are commercially available as nitric oxide donors. However, this assumption is in error and RSNO are stable compounds that require an additional agent to promote decomposition. This application proposes to investigate the molecular interactions of S-nitrosothiols with biological targets to understand more fully their role in biological systems. This will be done by addressing three hypothesis with associated specific aims: 1) The observations that protein thiols are the major intracellular targets of RSNO has led us to promote that the modification of protein thiol residues by RSNO is controlled by the local environment of the protein thiol. This specific aim will ask the crucial questions of what makes a particular thiol susceptible to control by RSNO: II) Our observations that heme proteins can directly reduce S-nitrosothiols have led us to propose that ferrous heme groups are a major site of RSNO metabolism. In this specific aim, we will explore the role played by heme moieties in the control of nitric oxide release from RSNO. III) Our observations concerning the metabolism of RSNO by endothelial cells has led us to propose that cells contain an active metabolic pathway for the metabolism of RSNO. These studiers will investigate the mechanism of RSNO metabolism by various cell types. The biochemistry of RSNO has been linked to asthma, inflammation, hypertension, apoptosis and atherosclerosis. It is envisioned that this study will yield new insights into the roles played by these important compounds and aid pharmacological development of new and more selectively potent S- nitrosothiols.