Slow detection reaction can mimic initial inhibition of an enzymic reaction

An analysis of sigmoid-shaped progress curves in the reaction between Elect ric Eel acetylcholinesterase (acetylcholine aeetylhydrolase, EC 3.1.1.7, AC hE) and its substrate acetylthiocholine in low concentrations at pH 7 is pr esented. In order to be able to explain an initial apparent inhibition of t he enzyme-substrate reaction, the rate of detection reaction had to be take n into account. The theoretical curves obtained by the fitting of different ial equations for the reaction mechanism to the data of six progress curves simultaneously, exactly reproduce the course of the experimental curves. T he measurements performed with various concentrations of detection reagent confirm the proposed cause of sigmoidity.