IN-VITRO INHIBITION OF HUMAN ERYTHROCYTE ACETYLCHOLINESTERASE (EC3.1.1.7) BY AN ANTINEOPLASTIC DRUG METHOTREXATE

This work addresses the kinetic analysis of the interaction of methotr exate (MTX) with human erythrocyte membrane-bound acetylcholinesterase (AChE, EC 3.1.1.7). It was found that the MTX effect was independent of time of incubation with AChE before the addition of substrate which proves its reversible action. The IC50 was determined, by three metho ds, to be 0.73 mM. The Michaelis-Menten constant (K-s) for the hydroly sis of acetylthiocholine iodide (ASCh) by AChE was 0.13 mM in the cont rol system, a value decreased by 30-61% in the MTX treated systems. Th e V-max was 1.27 mu mole/min/mg protein for the control system while i t was decreased by 44-77% in the MTX treated systems. The Lineweaver-B urk plot, Dixon plot, and their secondary replots indicated that the n ature of the inhibition was of the linear mixed type, i.e. uncompetiti ve and noncompetitive. The values of K-i(slope) and K-I(intercept) wer e estimated as 1.67 and 0.34 mM, respectively.