Activation of soluble guanylate cyclase by NO donors -: S-nitrosothiols, and dinitrosyl-iron complexes with thiol-containing ligands

We studied the capability of dimeric forms of dinitrosyl-iron complexes and S-nitrosothiols to activate soluble guanylate cyclase (sGC from human platelet cytosol. The dinitrosyl-iron complexes had the ligands glutathione (DNIC-GS) or N-acetylcysteine (DNIC-NAC). The S-nitrosothiols were S-nitrosoglutathione (GS-NO) or S-nitrosoacetylcysteine (SNAC). For both glutathione and N-acetylcysteine, the DNIC and S-nitrosothiol forms are equally effective activators of sGC. The activation mechanism is strongly affected by the presence of intrinsic metal ions. Pretreatment with the potent iron chelator, disodium salt of bathophenanthroline disulfonic acid (BPDS), suppressed sGC activation by GS-NO: the concentration of GS-NO producing maximal sGC activation was increased by two orders of magnitude. In contrast, activation by DNIC-GS is strongly enhanced by BPDS. When BPDS was added 10 min after supplementation of DNIC-GS or GS-NO at 4degreesC, it exerted a similar effect on sGC activation by either NO donor: BPDS only enhanced the sGC stimulation at low concentrations of the NO donors. Our experiments demonstrated that both Fe2+ and Cu2+ ions contribute to the decomposition of GS-NO in the presence of ascorbate. The decomposition of GS-NO induced by Fe2+ ions was accompanied by formation of DNIC. BPDS protected GS-NO against the destructive action of Fe2+ but not CU2+ ions. Additionally, BPDS is a sufficiently strong chelator to remove the iron from DNIC-GS complexes. Based on our data, we propose that S-nitrosothiols activate sGC via a two-step iron-mediated process: In the first step, intrinsic Fe2+ ions catalyze the formation of DNICs from S-nitrosothiols. In the secondary step, these newly formed DNICs act as the real NO donors responsible for sGC activation. (C) 2003 Elsevier Science (USA). All rights reserved.