title: Kinetics and equilibria of S-nitrosothiol-thiol exchange between glutathione, cysteine, penicillamines and serum albumin.
abstract: The kinetics and equilibria of S-nitrosothiol-thiol (SNO-SH) exchange reactions were determined using differential optical absorption. At pH 7.4 and 37 degrees C, k2 values ranged from 0.9 M-1.s-1 for the reaction between S-nitroso-glutathione (GSNO) and N-acetyl-penicillamine, and up to 279 M-1.s-1 for the exchange between S-nitroso-penicillamine (penSNO) and GSH. SNO-SH exchange involving GSH/GSNO and cysteine/cySNO was relatively rapid, k2 approx. 80 M-1.s-1 with an equilibrium constant slightly in favour of GSNO. GSNO was strongly favoured in equilibrium with penSNO, keq 0.0039. In the case of SNO-SH exchange between S-nitroso human serum albumin (albSNO) and GSH or cysteine k2 values were 3.2 and 9.1 M-1.s-1, respectively. The results show that the initial rate of SNO-SH exchange between physiological albSNO (7 microM) and venous plasma levels of GSH and cysteine is very slow, < 1%/min. On the other hand, if a nitrosothiol such as cySNO were to enter a cell, it would be rapidly converted to GSNO (43%/s).
authors.affiliation: Department of Biochemistry and Molecular Biology, University College, London, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Meyer
authors.forename: H
authors.initials: H
authors.lastname: Kramer
authors.forename: N
authors.initials: N
authors.lastname: Ozer
authors.forename: B
authors.initials: B
authors.lastname: Coles
authors.forename: B
authors.initials: B
authors.lastname: Ketterer
mesh_terms: D003545:Cysteine / Q000737:chemistry* / Q000378:metabolism; D005978:Glutathione / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009603:Nitroso Compounds / Q000737:chemistry* / Q000378:metabolism; D010396:Penicillamine / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism; D026422:S-Nitrosoglutathione; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism; D013997:Time Factors
chemical_list: D009603:Nitroso Compounds; D012709:Serum Albumin; D026422:S-Nitrosoglutathione; C010005:N-acetylpenicillamine; C024942:S-nitrosopenicillamine; D005978:Glutathione; D010396:Penicillamine; D003545:Cysteine