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

The kinetic parameters of the inhibition of pigeon brain acetylcholine sterase (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 Mic haelis-Menten constant (K-m) for the hydrolysis of acetylthiocholine i odide was found to be 1.53 x 10(-4) M and the V-max was 1.06 mu mol mi n(-1) mg(-1) protein. Dixon as well as Lineweaver-Burk plots and their secondary replots indicated that the nature of the inhibition is of t he linear mixed type which is considered to be a mixture of partial co mpetitive 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 b inding for the peripheral than for the active site.