Acetylcholinesterase turnover number

Acetylcholinesterase is subject to substrate Inhibition at high concentrations, but Mlchaells kinetics are observed at lower concentrations, because the substrate constant and the Mlchaells constant differ by a factor of 100. Turnover numbers run about 2-9 x 10 min l, and (Mlchaells constant) values are about 0.2 mM.76,116 Whatever the source, the enzyme is subject to inhibition by the same reversible and irreversible inhibitors. Most of the kinetic work has been done with the saline-extracted 11S enzyme from electric eel and the detergent-extracted 6S enzyme from erythrocytes. The former Is a tetramer derived from the native enzyme by the action of proteases the latter is a dimer. 

Cohen, J.A., Oosterbaan, R.A., Warringa, M.G.P.J. (1955). The turnover number of ali-esterase, pseudo- and tme cholinesterase and the combination of these enzymes with diisopro-pylfluorophosphonate. Biochim. Biophys. Acta 18 228-35. Coult, D.B., Marsh, D.J., Read, G. (1966). Dealkylation studies on inhibited acetylcholinesterase. Biochem. J. 98 869-73. 

Speed and efficiency mailer. Acetylcholine is rapidly de-Stroyetl l v the en/yme acetylcholinesterase. T his enzyme, which has a turnover number of 25,000 per second, has attained catalytic perfection with a of 2 X 10 M s V Why is the... 

Molecular Activity. Many enzymes have thus far been isolated in pure and crystallized form. In these cases, the molecular activity can be determined it is defined as the number of molecules of substrate transformed per minute per molecule of enzyme (or the number of mmoles of substrate per mole of enzyme, i.e. the number of enzyme units p er Mmole of enzyme). The term turnover number" has also been applied to this definition ( nd similar ones). For the calculation of molecular activity, the activity of the enzyme and its molecular weight must be known. A large molecular activity indicates a rapid reaction. Very large molecular activities have been found in the cases of acetylcholinesterase (18 X 10 ). The usual values range from several thousand to ten thousand molecules of substrate per enzyme molecule per minute, still a rather rapid turnover. 

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