OXIME REACTIVATION STUDIES OF INHIBITED TRUE AND PSEUDO CHOLINESTERASE

Abstract

Electric eel cholinesterase and purified pseudo cholinesterase from horse serum were inhibited with sarin, tabun, or O, O-diethyl-S-2-diethylaminoethyl phosphorothiolate. The inhibited enzymes were then reactivated at 25 °C with one of the oximes: pyridine 2-aldoxime methiodide, 1, 1′-trimethylene bis (4-hydroximinomethyl pyridinum) bromide, and 1-(3-triethylammoniopropyl)-4-hydroximinomethyl pyridinium dibromide. Two kinetically different types of reactivation were found; in one, reactivation was progressive with time, while in the other it was rapid initially followed by an equilibrium condition which was dependent upon the concentration of uninhibited enzyme in the system. The type of reactivation varied according to the nature of the enzyme, oxime, or inhibitor under investigation. Reactivation was always found to be dependent upon the concentration of oxime and inhibited enzyme, pH, and the presence of substrate. The rate of change at 25 °C of the inhibited enzymes to a form incapable of being reactivated has been assessed.