S-transnitrosation reactions are involved in the metabolic fate and biological actions of nitric oxide

S-Nitrosothiols are a group of potent, bioactive compounds that form through the reaction of nitric oxide (NO) with thiols in the presence of oxygen. These compounds ate naturally occurring in vivo, stabilize NO and potentials its biological effects, S-nitrosoglutathione is the most abundant intracellular S-nitrosothiol, and the kinetics far its information favors de novo synthesis, In this analysis, we studied the formation of S-nitrosothiols by S-transnitrosation, or exchange of -NO for -H between sulfur atoms; we synthesized S-nitroso-glutathionyl-Sepharose 4B beads (SNO-4B) as a reagent with which to measure S-transnitrosation reactions. We detected a maximum of 1.57 +/- 0.24 pmol NO/bead (n = 5) after S-nitrosation of the beads with acidified nitrite. The stability of the S-NO bond was dependent on temperature, but no PH over the 5 to range (except at pH 9 at 37 degrees), with an estimated t(1/2) of 30 hr at 22 degrees C and of approximately 2 wk at 4 degrees C. We demonstrated that SNO-4B transfers -NO to glutathione and to cysteine rapidly and in a pH-dependent manner. The initial rate of transfer of -NO from SNO-4B to glutathione at room temperature was 0.53, 3.03 and 5.14 mu M\min at pH 5.0, 7.4 and 9.0, respectively (P < .05), Under the same conditions, the initial rate of -NO transfer to cysteine was 0.72, 3.71 and 4.69 mu M/min at pH 5.0, 7.4 and 9.0, respectively (P < .05), There was no appreciable S-transnitrosation between SNO-4B and bovine serum albumin. We further demonstrated that SNO-4B evokes significant vasodilator and platelet inhibitory responses in plasma-free systems and activates platelet soluble guanylyl cyclase, These data suggest a mechanism by which to explain the metabolic fate and distribution of NO am fong thiol pools in the vasculature, and implicate S-transnitrosation at the cell surface in NO signal transduction.