Leaving group effects in butyrylcholinesterase reaction with organophosphorus inhibitors

The kinetic constants k2, KQ and the second-order rate constant ki of butyrylcholinesterase (acylcholine acylhydrolase, EC 3.1.1.8) inhibition by organophosphorus compounds (C2H5O)2P(O)SX, with both ionic and non-ionic substituents X, were determined at 25 degrees C and pH 7.5 in 0.15 M KCl. The data were analysed in terms of structure-activity relationships and the roles of the leaving group inductive effect and hydrophobicity in the enzyme specificity were established. This made possible calculations of the actual contribution of the substituent ionic charge in the effectivenes of butyrylcholinesterase action. On the basis of the structure-activity relationships for butyrylcholinesterase and acetylcholinesterase the specificities of the enzymes are compared and some common features are discussed.