title: Mechanism and stoichiometry of 2,2-diphenyl-1-picrylhydrazyl radical scavenging by glutathione and its novel alpha-glutamyl derivative.
abstract: Kinetic mechanism and stoichiometry of scavenging the 2,2-diphenyl-1-picrylhydrazyl radical by glutathione and its novel analog, containing alpha-glutamyl residue in place of the gamma-glutamyl moiety, were studied using different ratios of reagents. At low concentrations of the peptides, the process was described as a bimolecular reaction obeying the stoichiometric ratio 1:1. However, at excess of peptides the formation of a non-covalent complex between the reagents was discovered and characterized by dissociation constants K = 0.61 mM for glutathione and K = 0.27 mM for the glutathione alpha-glutamyl analog, respectively. The complex formation was followed by a reaction step that was characterized by the similar rate constant k = 0.02 s(-1) for both peptides. Thus, the apparently different antioxidant activity of these two peptides, observed under common assay conditions, was determined by differences in the formation of this non-covalent complex.
authors.affiliation: Institute of Chemistry, University of Tartu, 51014 Tartu, Estonia.
authors.forename: Säde
authors.initials: S
authors.lastname: Viirlaid
authors.forename: Riina
authors.initials: R
authors.lastname: Mahlapuu
authors.forename: Kalle
authors.initials: K
authors.lastname: Kilk
authors.forename: Aleksei
authors.initials: A
authors.lastname: Kuznetsov
authors.forename: Ursel
authors.initials: U
authors.lastname: Soomets
authors.forename: Jaak
authors.initials: J
authors.lastname: Järv
mesh_terms: D001713:Biphenyl Compounds / Q000737:chemistry*; D016166:Free Radical Scavengers / Q000737:chemistry* / Q000378:metabolism; D005978:Glutathione / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism; D007202:Indicators and Reagents / Q000737:chemistry; D007700:Kinetics; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry; D010851:Picrates / Q000737:chemistry*
chemical_list: D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D010455:Peptides; D010851:Picrates; C004931:1,1-diphenyl-2-picrylhydrazyl; D005978:Glutathione