Kinetics of the Inhibition of Acetylcholinesterase from Desert Cobra (Walterznnesza Aegyptza) Venom by Local Anesthetics: Procaine and Tetracaine

Abstract

The kinetic parameters of W aegyptia venom acetylcholinesterase (ACE) inhibition by procaine and tetracaine hydrochloride were investigated in the present study. Procaine and tetracaine reversibly inhibited the AChE activity in a concentration-dependent manner, the IC₅₀ being about 0.28 and 0.04 mM, respectively. The Michaelis-Menten constant (K_m) for the hydrolysis of acetylthiocholine iodide was found to be 0.051 mM with V_max 10.2 μ;mole/min/mg protein. Both K_M and V_max were affected by procaine while only V_max decreased with tetracaine. A Lineweaver-Burk plot and its secondary replot indicated that the nature of the inhibition is of the linear mixed type for procaine which is considered to be a mixture of competitive and noncompetitive types while the inhibition was noncompetitive for tetracaine. The values of K_i(slope) and K_I(intercept were estimated as 0.133 mM and 0.451 mM for procaine and 7.2 × 10⁻-³ mM for tetracaine, respectively, by the secondary replots of the Lineweaver-Burk plot.

Key Words: :

• Acetylcholinesterase
• procaine
• tetracaine
• kinetics
• inhibition
• venom