Iron catalyzes both decomposition and synthesis of S-nitrosothiols: optical and electron paramagnetic resonance studies.
Formation of S-nitrosothiols was demonstrated in 1-50 mM aqueous solutions of cysteine or glutathione (cys-NO or GS-NO, respectively) upon contact of thiols with gaseous nitric oxide under a pressure of 50-600 mm Hg and anaerobic conditions. The yield of S-nitrosothiols was increased by mixing with NO plus air at a molar ratio [NO]/[O2 from air] of no less than 40. In this instance, the S-nitrosothiol formation was optimum at a NO pressure of 100-150 mm Hg. The addition of 0.25 mM o-phenanthroline, a selective Fe2+ chelator, to thiol solutions prior to the treatment with NO or NO + air completely blocked the formation of S-nitrosothiols. On the other hand, this process was potentiated by the addition of Fe2+ but not Cu2+ ions. These data indicated a crucial influence of Fe2+ on the process. The contact of o-phenanthroline with S-nitrosothiols synthesized by a routine method (treatment of thiol solutions with the NO + NO2 mixture at pH <1) did not induce their degradation at pH 3-10. Moreover, o-phenanthroline strikingly enhanced the cys-NO stability at neutral pH. Cysteine, glutathione, and desferal, a selective Fe3+ chelator, exerted a similar effect on cys-NO. The stabilizing effect of thiols on cys-NO was accompanied by the formation of dinitrosyl-iron complexes with thiol-containing ligands containing admixed (intrinsic) iron (1-2 microM). The addition of Fe2+ at a concentration higher than 10 microM abolished the stabilizing effect of thiols on cys-NO. Therefore iron can induce both degradation and synthesis of S-nitrosothiols. According to the proposed mechanisms such opposite effects of iron on S-nitrosothiols are determined by the ratio between S-nitrosothiols, thiols, iron, and NO in the reaction system.
Vanin
A F
AF
Institute of Chemical Physics, Russian Academy of Sciences, Moscow.
Malenkova
I V
IV
Serezhenkov
V A
VA
D002384:Catalysis; D003545:Cysteine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005978:Glutathione / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D009603:Nitroso Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D026422:S-Nitrosoglutathione; D026403:S-Nitrosothiols; D012710:Serum Albumin, Bovine / Q000737:chemistry
D006454:Hemoglobins; D009603:Nitroso Compounds; D026403:S-Nitrosothiols; D012710:Serum Albumin, Bovine; D026422:S-Nitrosoglutathione; C021315:S-nitrosocysteine; D007501:Iron; D005978:Glutathione; D003545:Cysteine