Local dynamics of GSTA1-1 near the catalytic Tyr-9. Left: In the apo hGSTA1-1, Phe-10 (black) is above Tyr-9 (black), and the C-terminus is disordered (not visible). Upon addition of the ethacrynic acid conjugate GS–EA, Phe-10 moves to allow Phe-220 within the C-terminal helix to occupy the space above Tyr-9 (structures taken from refs 16 and 17). Right: The Phe-10/Tyr-9 interaction in the rGSTA1-1·GSO3− complex (18) is similar to that of the human isoform, except the Phe-10 makes a steeper angle with, and is closer to, the center of the aromatic ring of Tyr-9.