Transient kinetics of the acetylcholinesterase catalyzed hydrolysis of N-methylindoxyl acetate.
An experimental study has been made of the kinetics of the hydrolysis of N-methylindoxyl acetate catalyzed by electric-eel acetylcholinesterase, both in the steady state and the pre-steady statemstopped-flow and temperature-jump experiments revealed a fast transient and a slow one. The fast transient is correlated with the conventional mechanism E+A in equilibrium EA yields X-yieldsEA' YIELDS E+Y. The slow transient is attributed to conformational changes involving E or EA. Analysis of it revealed two exponential terms of the form e- minus lambda t, and the two lambda values were obtained over the temperature range 5Yand 25Ydegrees C. The results are interpreted in terms of two alternative mechanisms; in one, the enzyme undergoes a conformational change before it adds on the substrate molecule; in the other, the conformational change occurs after the substrate addition. Both mechanisms may be involved, but the results exclude a concerted mechanism in whivh the conformational change occurs concurrently with the addition of substrate. Kinetic parameters (delta S not equal to and E) are obtained for this conformational change and for the conversion of EA into EA'+X.
D000085:Acetates; D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D004593:Electrophorus; D007211:Indoles; D007700:Kinetics; D008433:Mathematics; D013696:Temperature; D013997:Time Factors
D000085:Acetates; D007211:Indoles; D000110:Acetylcholinesterase