Rational modulation of the catalytic activity of A1-1 glutathione S-transferases: evidence for incorporation of an on-face (pi...HO-Ar) hydrogen bond at tyrosine-9

The solid-state kinetics, site-directed mutagenesis, fluorescence and ultraviolet spectroscopies, ab initio calculations and molecular modeling were employed to examine the cofactor glutathione (GSH) in contact with the active site of rat A1-1 glutathione S-transferase. Specifically, it was found that the pKa of the cofactor decreases after PHe-220 was replaced by Tyr-9 due to the generation of an on-face Ar-OH-pi hydrogen bond.