Spontaneous reactivation of acetylcholinesterase following organophosphate inhibition: II. Characterization of the reactivating components

Abstract

Repeated cycles of inhibition by a variety of organophosphates followed by spontaneous reactivation reveal a component of electric eel by acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) which preferentially reactivates. That the observed enzymatic activity truly resides in acetylcholinesterase is indicated by its sensitivity to a specific inhibitor and by molecular weights for subunits and native enzyme which are approximately the same as those for the major fraction of enzymatic activity which behaves in the classical manner. The K m values for phenyl acetate of the two components are similar but the rate constant for covalent bond formation, k 2, with isopropyl m-nitrophenyl methylphosphonate is greatly reduced in the spontaneously reactivating species. The molecular basis for these observations is discussed.