Iron is a catalyst of cysteine and glutathione S-nitrosation on contact with nitric oxide in aqueous solutions at neutral pH

S-Nitrosocysteine and S-nitrosoGSH were formed when cysteine or reduced glutathione in 15 mM Hepes-buffer contacted gaseous nitric oxide at neutral pH for 5 min under anaerobic conditions. On increasing the thiol concentration from 1 to 50 mM and the NO pressure from 50 to 700 mm Hg, higher yields of the S-nitrosothiols were observed. Simultaneously with the synthesis of S-nitrosothiols, dinitrosyl iron complexes (DNIC) between cysteine or GSH and trace iron ions were formed. The addition of 20 mu M Fe2+ stimulated the formation of both S-nitrosothiols and DNIC. The concentration of S-nitrosothiol formed was 40-50% of the initial thiol concentration. S-Nitrosothiol as well as DNIC formation with or without iron present was completely inhibited by preliminary treatment of the solutions with the selective Fe2+ chelating agent o-phenanthroline. Admixed or added iron was found to be a catalyst of S-nitrosothiol formation under these conditions. NO is transformed to NO+ ion which effectively nitrosates thiols in the presence of iron forming DNIC.