KINETICS OF THE INHIBITION OF ACETYLCHOLINESTERASE IN CAMEL RETINA BYCISPLATIN

The inhibitory effect of cisplatin (CDDP) on camel retina acetylcholin esterase (AChE) was characterized. The CDDP effect was independent of the time of incubation with AChE before the addition of substrate, ind icative of reversible inhibition. Moreover, dilution data prove that C DDP is a reversible inhibitor of camel retina AChE. Cisplatin inhibite d AChE activity of camel retina in a concentration-and time-dependent manner, the IC50 values being 5.32 and 0.196 mM at 5 min and 24 h incu bation times, respectively. The IC50 has dual components, i.e. directl y proportional and inversely proportional to 0-1.5 h and 1.5-24 h incu bation periods, respectively. The Michaelis-Menten constant (K-m) for the hydrolysis of acetylthiocholine iodide (ASCh) was found to be 0.07 96 mM and V-max was 0.668 mu mol/min/mg protein. K-mapp and V-maxapp b oth decreased as the CDDP concentration increased. Dixon as well as Li neweaver-Burk plots and their secondary replots indicated that the nat ure of the inhibition was of the pure uncompetitive type. The value of K-i was estimated as 0.811 mM by the primary and secondary replots of the Lineweaver-Burk and Dixon plots. K-iapp decreased while V-maxiapp increased after increasing the ASCh concentration. (C) 1998 Elsevier Science Ireland Ltd.