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 (ACh E) activity by tetrahydroaminoacridine (THA, tacrine) has been investi gated in the present study. The non-significant change of the percent inhibition of AChE by THA with respect to various lengths of the prein cubation period showed the type of the reversible inhibition. THA reve rsibly inhibited AChE activity in a concentration dependent manner; IC 50 was 0.23 mu M while the IC100 was 14.22 mu M. The K-m for the hydro lysis of acetylthiocholine iodide was found to be 62.6 mu M in the con trol system; a value increased in the THA treated systems. The V-max w as 0.472 mu mole/min/mg protein for the control system, while it decre ased in the THA treated systems. Dixon, as well as Lineweaver-Burk, pl ots and their secondary replots indicated that the nature of the inhib ition 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, res pectively. The K-i' was greater than K-i indicating that THA has a gre ater affinity of binding for the peripheral site than the active site of the camel retina AChE. The use of camel retina as a good experiment al animal model may open new avenues for studying acetylcholine and AC hE metabolism.