Evaluation of the Nature of Camel Retinal Acetylcholinesterase: Inhibition by Hexamethonium

Abstract

Acetylcholinesterase (AChE, EC 3.1.1.7) has been demonstrated in retinas of several species, however, the nature of the interaction of AChE with specific inhibitors are very limited in the literature and the mode of inhibition of camel retinal AChE by hexamethonium has been studied. Hexamethonium reversibly inhibited AChE in a concentration dependent manner, the IC₅₀ value being c. 2.52 mM. The K_m for the hydrolysis of acetylthiocholine iodide was found to be 0.087 mM and the V_max was 0.63 μmol/min/mg protein. Dixon, as well as Lineweaver-Burk, plots and their secondary replots indicated that the nature of the inhibition is of the hyperbolic (partial) mixed type, which is considered to be a partial competitive and non-competitive mixture. The values of K_i(slope) and K_i(intercept) from a Lineweaver-Burk plot were estimated as 0.30 mM and 0.17 mM, respectively, while K_i from a Dixon plot was estimated as 0.725 mM. The K_i was greater than K_i indicating that hexamethonium has a greater affinity of binding for the active site than the peripheral site of the camel retina AChE.

Key Words: :

• Acetylcholinesterase
• Inhibition
• Hexamethonium
• Retina
• Kinetics