The nature of the inhibition of camel retina acetylcholinesterase (EC 3.1.1.7) activity by tetrahydroaminoacridine

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 mu M while the IC100 was 14.22 mu M. The K-m for the hydrolysis of acetylthiocholine iodide was found to be 62.6 mu M in the control system; a value increased in the THA treated systems. The V-max was 0.472 mu mole/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 mu M and 0.181 mu M, 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.