Test 2558 2406

is a noncompetitive inhibitor of TcAChE, competing with reversible inhibitors directed at both ‘‘anionic’’ subsites, but a single site is involved in inhibition. The crystal structure reveals a single , oriented down the gorge toward the CAS (2w9i); it is plausible that irreversible inhibition is associated with photooxidation of this residue and others within the active-site gorge.