title: Tyrosine-7 in human class Pi glutathione S-transferase is important for lowering the pKa of the thiol group of glutathione in the enzyme-glutathione complex.
abstract: Previously, we reported the importance of Tyr7 for the catalytic activity of human class Pi glutathione S-transferase [Kong et al. (1992) Biochem. Biophys. Res. Comm., 182, 1122]. As an extension of this study, we investigated the pH dependence of kinetic parameters of the wild-type enzyme and the Y7F mutant. The replacement of Tyr7 with phenylalanine was found to alter the pH dependence of Vmax and Vmax/KmCDNB of the enzyme for conjugation of GSH with 1-chloro-2,4-dinitrobenzene (CDNB). The pKa of the thiol of GSH in the wild-type enzyme-GSH complex was estimated to be about 2.4 pK units lower than that in the Y7F-GSH complex. Tyr7 is thus considered to be important for catalytic activity in lowering the pKa of the thiol of GSH in the enzyme-GSH complex.
authors.affiliation: Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Japan.
authors.forename: K H
authors.initials: KH
authors.lastname: Kong
authors.forename: K
authors.initials: K
authors.lastname: Takasu
authors.forename: H
authors.initials: H
authors.lastname: Inoue
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D014443:Tyrosine
chemical_list: D007527:Isoenzymes; D014443:Tyrosine; D005982:Glutathione Transferase; D005978:Glutathione