KINETICS OF THE INHIBITION OF ACETYLCHOLINESTERASE FROM DESERT COBRA (WALTERINNESIA-AEGYPTIA) VENOM BY LOCAL-ANESTHETICS - PROCAINE AND TETRACAINE

The kinetic parameters of W. aegyptia venom acetylcholinesterase (AChE ) inhibition by procaine and tetracaine hydrochloride were investigate d in the present study. Procaine and tetracaine reversibly inhibited t he AChE activity in a concentration-dependent manner, the IC50 being a bout 0.28 and 0.04 mM, respectively. The Michaelis-Menten constant (K- m) for the hydrolysis of acetylthiocholine iodide was found to be 0.05 1 mM with V-max 10.2 mu mole/min/mg protein. Both K-m and V-max were a ffected by procaine while only V-max decreased with tetracaine. A Line weaver-Burk plot and its secondary replot indicated that the nature of the inhibition is of the linear mixed type for procaine which is cons idered to be a mixture of competitive and noncompetitive types while t he inhibition was noncompetitive for tetracaine. The values of K-i(slo pe) and K-l(intercept were estimated as 0.133 mM and 0.451 mM for proc aine and 7.2 x 10(-3) mM for tetracaine, respectively, by the secondar y replots of the Lineweaver-Burk plot.