KINETICS OF THE INHIBITION OF ACETYLCHOLINESTERASE FROM PIGEON BRAIN BY PROCAINE HYDROCHLORIDE

The kinetic parameters of the inhibition of pigeon brain acetylcholinesterase (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 (K-m) for the hydrolysis of acetylthiocholine iodide was found to be 1.53 x 10(-4) M and the V-max was 1.06 mu mol 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 K-i(slope) and K-i (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 K-i(')/K-i ratio shows that procaine has a greater affinity of binding for the peripheral than for the active site.