ACTIVATION OF SOLUBLE GUANYLYL CYCLASE BY THE NITROVASODILATOR 3-MORPHOLINOSYDNONIMINE INVOLVES FORMATION OF S-NITROSOGLUTATHIONE

Soluble guanylyl cyclase (sGC) is the major physiological target of sy dnonimine-based vasodilators such as molsidomine. Decomposition of syd nonimines results in the stoichiometric formation of nitric oxide (NO) and superoxide (O-2(radical anion)) which rapidly react to form perox ynitrite. Inasmuch as sGC is activated by NO but not by peroxynitrite, we investigated the mechanisms underlying sGC activation by 3-morphol inosydnonimine (SIN-1). Stimulation of purified bovine lung sGC by SIN -1 was found to be strongly dependent on glutathione (GSH). By contras t, GSH did not affect sGC activation by NO released from 2,2-diethyl-1 -nitroso-oxyhydrazine, indicating that NO/O-2(radical anion) released from SIN-1 converted GSH to an activator of sGC. High performance liqu id chromatography identified this product as the thionitrite S-nitroso glutathione. Further, the reaction product decomposed to release NO up on addition of Cu(NO3)(2) in the presence of GSH. Activation of sGC wa s antagonized by the Cu(I)-specific chelator neocuproine, whereas the Cu(II)-selective drug cuprizone was less potent. Carbon dioxide (deliv ered as NaHCO3) antagonized S-nitrosation by peroxynitrite but not by SIN-1. Thus, NO/O-2(radical anion) released from SIN-1 mediates a CO2- insensitive conversion of GSH to S-nitrosoglutathione, a thionitrite t hat activates sGC via trace metal-catalyzed release of NO. These resul ts may provide novel insights into the molecular mechanism underlying the nitrovasodilator action of SIN-1.