Fig. (4) Structure model of H272F bound covalently to the TMR-ligand. Ligand was manually docked into H272F and bonded to the nucleophile Asp106. Phe272 lies in proximity to the bond but is unable to act as a general base and catalyze hydrolysis. Other residues of interest in close proximity to ligand include Lys175, Cys176, and Tyr273.