[Stereospecificity of active centers of acylcholinesterases]

The stereospecificity of the active center of acetylcholinesterase from human erythrocytes (AChE) and butyrylcholinesterase from horse blood serum (BuChE) in reactions with enantiomers of irreversible organophosphorus inhibitors (OPI) with asymmetrical central phosphorus atom and different structure of the leaving moiety: C2H5O(CH3)P(O)SR, where R = C2H7; C6H13: C4H4SC2H5; C2H4SC2H5 and C2H4S(CH3)C2H5, was studied. The strongest inhibiting effect with respect to cholinesterases was exerted by (-)-isomers of the OPI tested. The differences in the inhibiting activity of (-) and (+)-isomers were especially well-pronounced for OPI with R = C3H7 and C4H4SC2H5. The differences in the inhibiting activity of the enantiomers suggest that the stereospecificity of the active center of AChE was the highest and that of BuChE was considerably lower. After treatment by N,N-dimethyl-2-phenylaziridinium ions which specifically and irreversibly modify the anionic groups on the active surface of AChE, the stereospecificity of the latter is decreased and is approximated to that of BuChE. The differences in stereospecificity of AChE and BuChE are probably due to the considerable differences in the spatial structure of the enzyme active centers.