Sensitivity of bovine retinal acetylcholinesterase (E.C. 3.1.1.7) toward tacrine: kinetic characterization.

This work addresses the kinetic analysis of the interaction of tacrine with bovine retina acetylcholinesterase (A ChE, E.C. 3.1.1.7). It was found that the tacrine effect was reversible in nature. Tacrine inhibited bovine retinal AChE activity in a concentration-dependent manner; IC50 was fo to be 8.07 nM. The Michaelis-Menten constant (Ka) for the hydrolysis of acetylthiocholine iodide (ASCh) by AChE was 0.061 mM in the control system, and this value was increased by 54-67% in the tacrine-treated systems. The Vmax was 0.701 mumole/min per milligram protein for the control system, but it was decreased by 26-69% in the tacrine-treated systems. The Lineweaver-Burk plot, Dixon plot, and their secondary replots indicated that the nature of the inhibition was of the partial mixed type, that is, a mixture of competitive and noncompetitive inhibition. The values of Ki and Kt were estimated to be as 4.475 and 8.517 nM, respectively.