title: Mutation of an evolutionarily conserved tyrosine residue in the active site of a human class Alpha glutathione transferase.
abstract: Human class Alpha glutathione transferase (GST) A1-1 has been subjected to site-directed mutagenesis of a Tyr residue conserved in all classes of cytosolic GSTs. The change of Tyr8----Phe lowers the specific activities with three substrates to 2-8% of the values for the wild-type enzyme. The changes in the kinetic parameters kcat/KM, Vmax and S0.5 show that the decreased activities are partly due to a reduced affinity for glutathione. The effect is reflected in lowered kcat values, suggesting that the hydroxyl group of Tyr8 is involved in the activation of glutathione. The proposal of such a role for the Tyr residue has support from the 3D structure of a pig lung class Pi GST [Reinemer et al. (1991) EMBO J. 10, 1997-2005]. Thus, Tyr8 appears to be the first active site residue established as participating in the chemical mechanism of a GST.
authors.affiliation: Department of Biochemistry, Uppsala University, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Stenberg
authors.forename: P G
authors.initials: PG
authors.lastname: Board
authors.forename: B
authors.initials: B
authors.lastname: Mannervik
mesh_terms: D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002384:Catalysis; D004789:Enzyme Activation; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D006801:Humans; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D013379:Substrate Specificity; D014443:Tyrosine / Q000235:genetics*
chemical_list: D014443:Tyrosine; D005982:Glutathione Transferase; D005978:Glutathione