PURIFICATION AND PROPERTIES OF THE INDUCIBLE CHOLINESTERASE OF PSEUDOMONAS FLUORESCENS (GOLDSTEIN)

Abstract

The inducible cholinesterase produced by the Goldstein strain of Pseudomonas fluorescens was purified to a state of electrophoretic homogeneity. The enzyme, which resembles an acetylcholinesterase in its substrate specificity, has a high affinity for acetylcholine and propionylcholine. The estimated values of Kmat pH 7.4 and 37 °C are 1.4 × 10−5 M for acetylcholine and 2.0 × 10−5 M for propionylcholine. The bacterial cholinesterase reacts very slowly with tetraethyl pyrophosphate (TEPP) and diisopropyl phosphorofluoridate (DFP) but comparatively rapidly with ethyl N,N-dimethylphosphoramidocyanidate (Tabun). Bimolecular rate constants range from 7.7 mol−1min−1for TEPP to 7.4 × 104 mol−1min−1for Tabun. The reactions of the cholinesterase depend upon the ionic state of groups in the enzyme whose pKavalues are in the same range as those reported for other esterases. The results suggest that the enzyme may be similar in structure to other cholinesterases, and that both histidine and serine may be involved in its activities.