Kinetic analysis of the toxicological effect of tacrine (Cognex (R)) on human retinal acetylcholinesterase activity

For the first time, kinetic parameters of the effect of tacrine, an anti-ch olinesterase inhibitor of therapeutic potential in Alzheimer's disease has been studied on human retinal acetyl-cholinesterase (AChE). Tacrine inhibit ed the AChE activity in a concentration dependent manner, the IC50 being ab out 45 nM. The Michaelis-Menten constant (K-m) for the hydrolysis of acetyl thiocholine iodide was found to be 0.120 mM and this value was increased by 4-52.8% in the presence of tacrine. V-max was observed to be 2.73 mu mol/h per mg protein for the control system, while it was decreased by 14.73-56. 25% in the tacrine treated systems. Dixon as well as Lineweaver-Burk plots and their secondary replots indicated that the nature of the inhibition was of the mixed type, i.e. a combination of competitive and noncompetitive in hibition. The values of K-i and K-l were estimated to be as 37.76 and 64.36 nM, respectively. (C) 2000 Elsevier Science Ireland Ltd. All rights reserv ed.