Kinetics of the inhibition of acetylcholinesterase from pigeon brain by procaine hydrochloride

Abstract

The kinetic parameters of the inhibition of pigeon brain acetylchlolinesterase (AChE) by procaine hydrochloride were investigated. Procaine (0·083–1·67 mM) reversibly inhibited AChE activity (15–83 percent) in a concentration dependent manner, the IC50 being about 0·38 mM. The Michaelis-Menten constant (Km) for the hydrolysis of acetylthiocholine iodide was found to be 1·53 × 10−4 M and the Vmax was 1·06 μmol min−1 mg−1 protein. Dixon as well as Lineweaver-Burk plots and their secondary replots indicated that the nature of the inhibition is of the linear mixed type which is considered to be a mixture of partial competitive and pure non-competitive. The values of Ki(slope) and Ki (intercepts) were estimated as 0·14 mM and 0·22 mM respectively by the primary Dixon and by the secondary replots of the Lineweaver-Burk plot. The Ki′/Ki ratio shows that procaine has a greater affinity of binding for the peripheral than for the active site.