Superoxide-mediated decomposition of biological S-nitrosothiols.
Incubation of S-nitrosocysteine or S-nitrosoglutathione (5-100 M) in the presence of a generator of superoxide (xanthine/xanthine oxidase) resulted in a time-dependent decomposition of S-nitrosothiols and accumulation of nitrite/nitrate in reaction mixtures. Quantitatively, the amounts of nitrite/nitrate represented >90% of nitrosonium equivalent of S-nitrosothiols degraded during the incubation. The reaction rates were unaffected by the presence catalase (1 unit/ml). Kinetic analysis showed that the degradation of S-nitrosothiols in the presence of superoxide proceeded at second order rate constants of 76,900 M-1 s-1 (S-nitrosocysteine) and 12,800 M-1 s-1 (S-nitrosoglutathione), respectively, with a stoichiometric ratio of 1 mol of S-nitrosothiol per 2 mol of superoxide. The findings provide the evidence for the involvement of superoxide in the metabolism of S-nitrosothiols. Furthermore, substantially slower reaction rates of superoxide with S-nitrosothiols relative to the reaction rate with NO are consistent with the contention that the transient formation of S-nitrosothiols in biological systems may protect NO from its rapid destruction by superoxide, thus enabling these compounds to serve as carriers or buffers of NO.
Aleryani
S
S
Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115, USA.
Milo
E
E
Rose
Y
Y
Kostka
P
P
D002374:Catalase / Q000378:metabolism; D003545:Cysteine / Q000031:analogs & derivatives* / Q000378:metabolism; D005978:Glutathione / Q000031:analogs & derivatives* / Q000378:metabolism; D008956:Models, Chemical; D009580:Nitroblue Tetrazolium / Q000378:metabolism; D009603:Nitroso Compounds / Q000378:metabolism*; D010084:Oxidation-Reduction; D026422:S-Nitrosoglutathione; D026403:S-Nitrosothiols; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*
D009603:Nitroso Compounds; D026403:S-Nitrosothiols; D013438:Sulfhydryl Compounds; D013481:Superoxides; D009580:Nitroblue Tetrazolium; D026422:S-Nitrosoglutathione; C021315:S-nitrosocysteine; D002374:Catalase; D005978:Glutathione; D003545:Cysteine