Investigation of the reversible inhibition of camel (Camelus dromedarius) acetylcholinesterase by tetracaine

Abstract

1. The camel erythrocyte membrane bound acetylcholinesterase (AChE) was extracted with the non-ionic detergent Triton X-100 and some of its kinetics parameters were studied. In addition the effect of tetracaine hydrochloride on AChE was also investigated.

2. The Michaelis-Menten constant (K_m) for the hydrolysis of acetylthiocholine iodide was found to be 7 × 10⁻⁵M and the V_max was 21.2 μmol/hr/mg protein.

3. Tetracaine (0.025–0.80 mM) reversibly inhibited the AChE activity (25–82%) in a concentration-dependent manner, the ic₅₀ being about 0.12 mM.

4. The Lineweaver-Burk plot and its secondary plots indicated that the nature of this inhibition is of the linear mixed type. This mixed type inhibition system is considered to be composed of partial competitive and pure non-competitive in nature.

5. The values of K_i(slope) and K_{ii(intercept)} were estimated as 0.127 mM and 0.263 mM, respectively, by a secondary replot of primary double reciprocal plot of Lineweaver-Burk plot and Dixon plot.

6. $\text{K}{}_{\mathrm{<mtext>ii</mtext>}}\text{K}{}_{\mathrm{<mtext>i</mtext>}}$ ratio shows that tetracaine has a greater affinity of binding to the active site than to a peripheral site.