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Acetyl Cholinesterase (AChE)

    (Acetylcholine acetylhydrolase; EC Acetyl Cholinesterase (AChE) catalyzes the hydrolysis of acetylcholine as shown below:

    Actylcholine + H2O Choline + Acetic Acid

    This enzyme is bound to cellular membranes and is believed to be associated with the conduction of nerve impulses. It has been isolated from various animal tissues, including the brain, lungs, and erythrocytes. A second cholinesterase is found in blood serum (butyryl cholinesterase; EC, which hydrolyzes butyrylcholine four times faster than acetylcholine. They are two distinct enzymes in terms of substrate specificity and pH optimum. The assay of these two enzymes is of diagnostic value in various liver diseases, malignancies and in pulmonary tuberculosis (Methods of Enzymatic Analysis, Bergmeyer, H.U. ed.,: Vol.2., 833, 1974, Academic Press, New York).

    The amount of enzyme causing the hydrolysis of one micromole of acetylthiocholine iodide per minute at 25 C and pH 8.0.

    The assay is based on measurement of the change in absorbance at 405 nm. The method is described in detail by Ellman, G. L., et al, Biochem. Pharmacol., 7, 88-95, 1961.

  1. 0.25 mM 51, 51 Dithiobis (2-Nitrobenzoic Acid) (0.10 mg/ml) in 0.05 M Tris-HCl, pH 8.0, containing 0.1 M NaCl and 0.02 MgCl2●6H2O.
  2. 0.033 M Acetylthiocholine Iodide (9.2 mg/ml) in H2O.
  3. Enzyme in 0.1% Albumin (in 0.05 M Tris-HCl, pH 8.0). Concentration of the enzyme 0.113 U/mg.

  1. Set spectrophotometer (equipped with strip chart recorder and temperature control) at 405 nm and 25 C.
  2. Into cuvettes pipette the following reagents as indicated:
    Dithiobis 2.70 ml
    Acetylthiocholine Iodide 0.20 ml
    Mix and incubate in spectrophotometer at 25 C for 5 min.
  3. Record the absorbance at 405 nm (blank).
  4. Initiate the reaction by addition of 0.1 ml enzyme solution.
  5. Record absorbance at 405 nm for 5 min.

Activity (U/mg) = (ΔE405nm/min)(Total Vol.)(Enz. Diln.)
(13.3)(Enz. Vol.)(mg Enz./ml)

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