Reversible inhibition of acetylcholinesterase and butyrylcholinesterase by4,4 '-bipyridine and by a coumarin derivative

Inhibition of recombinant mouse wild type AChE (EC 3.1.1.7) and BChE (EC 3. 1.1.8), and AChE peripheral site-directed mutants and human serum BChE vari ants by 4,4'-bipyridine (4,4'-BP) and the coumarin derivative 3-chloro-7-hy droxy-4-methylcoumarin (CHMC) was studied. The enzyme activity was measured with acetylthiocholine as substrate. Enzyme-inhibitor dissociation constan ts for the catalytic and peripheral sites were evaluated from the apparent dissociation constants as a function of the substrate concentration. Inhibi tion by 4,4'-BP of AChE, BChE and the AChE mutant Y72N/Y124Q/W286A, was con sistent with inhibitor binding to both catalytic and peripheral sites. The dissociation constants for the peripheral site were about 3.5-times higher than for the catalytic site. The competition between CHMC and substrate dis played two binding sites on the AChE mutants Y72N, Y124Q, W286A and W286R, and on the atypical and fluoride-resistant BChE variants. The dissociation constants for the peripheral site were on average two-times higher than for the catalytic site. CHMC displayed binding only to the catalytic site of Y 72N/ Y124Q/W286A mutant and only to the peripheral site of w.t. AChE and th e human usual BChE. Modelling of the 4,4'-BP and CHMC binding to wild type mouse AChE substantiated the difference between the inhibitors in their mod e of binding which was revealed in the kinetic studies. (C) 1999 Elsevier S cience Ireland Ltd. All rights reserved.