THE INHIBITORY EFFECT OF CYCLOPHOSPHAMIDE ON CAMEL RETINA ACETYLCHOLINESTERASE ACTIVITY

Kinetic parameters for the effect of cyclophosphamide (CP) on the came l retina acetylcholinesterase (AChE) activity were investigated for th e first time in the present study. It was found that 18 mu g of retina protein and an incubation time of 4.0 min were suitable conditions fo r linear of AChE activity. The CP effect was independent of time of in cubation with AChE before the addition of substrate, which shows its r eversible action. Moreover, dilution data prove that CP is a reversibl e inhibitor of camel retina AChE. Cyclophosphamide (0.2-2.4 mM) inhibi ted activity of camel retina in a concentration-dependent fashion, the IC50 being about 1.17 mM. The Michaelis constant (K-m) for the hydrol ysis of acetylthiocholine iodide was found to be 0.106 mM and the V-ma x was 0.765 mu mol/min/mg protein. Dixon as well as Lineweaver-Burk pl ots and their secondary replots indicated that the nature of the inhib ition was of the pure noncompetitive type. The value of K-i was estima ted as 0.763 mM by the primary Dixon and secondary replots of the Line weaver-Burk plot.