Inhibition of human acetylcholinesterase by cyclophosphamide.

The inhibitory effect of cyclophosphamide (CP) on human erythrocyte membrane bound acetylcholinesterase (AChE) was investigated in the present study. It was found that CP inhibits the AChE reversibly with an IC50 of 511 microM. The Michaelis-Menten constant (Km) was 132 microM for AChE in the control system; a value increased by 78% in the CP treated system. The Vmax was 73.8 mumol/h/mg protein for the control system. The Lineweaver-Burk plot and Dixon plot indicated that the nature of this inhibition is of the linear mixed type, i.e., partially competitive and purely noncompetitive. The values of Ki and KI were estimated as 378 and 582 microM, respectively. The KI was greater than Ki indicating that noncompetitive inhibition was predominant over competitive.