The Nature of the Inhibition of Camel Retina Acetylcholinesterase (EC 3.1.1.7) Activity by Tetrahydroaminoacridine

Abstract

ABSTRACT

The nature of the inhibition of camel retina acetylcholinesterase (AChE) activity by tetrahydroaminoacridine (THA, tacrine) has been investigated in the present study. The non-significant change of the percent inhibition of AChE by THA with respect to various lengths of the preincubation period showed the type of the reversible inhibition. THA reversibly inhibited AChE activity in a concentration dependent manner; IC₅₀ was 0.23 μM while the IC₁₀₀ was 14.22 μM. The K_m for the hydrolysis of acetylthiocholine iodide was found to be 62.6 μM in the control system; a value increased in the THA treated systems. The V_max was 0.472 μmole/min/mg protein for the control system, while it decreased in the THA treated systems. Dixon, as well as Lineweaver-Burk, plots and their secondary replots indicated that the nature of the inhibition is of the linear mixed type, which is considered to be a partial competitive and pure non-competitive mixture. The values of K_i(slope) and K′_i(intercept) were estimated as 0.068 μM and 0.181 μM, respectively. The K′_i was greater than K_i indicating that THA has a greater affinity of binding for the peripheral site than the active site of the camel retina AChE. The use of camel retina as a good experimental animal model may open new avenues for studying acetylcholine and AChE metabolism.