Tyrosine-7 is an Essential Residue for the Catalytic Activity of Human Class Pi Glutathione S-Transferase: Chemical Modification and Site-directed Mutagenesis Studies

Abstract

The glutathione (GSH)-conjugating activity of human class Pi glutathione S-transferase (GSTπ) toward 1-chloro-2,4-dinitrobenzene (CDNB) was significantly lowered by reaction with N-acetylimidazole, an O-acetylating reagent for tyrosine residues. Further, the replacement of Tyr7 in GSTπ, which is conserved in all cytosolic GSTs, with phenylalanine by sitedirected mutagenesis also lowered the activities toward CDNB and ethacrynic acid. The Km values of the mutant for both GSH and CDNB were almost equivalent to those of the wild type, while the Vmax of the former was about 55-fold smaller than that of the latter. Therefore, Tyr7 is considered to be an essential residue for the catalytic activity of GSTπ.