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Butyryl Cholinesterase (BChE)

(Acylcholine acylhydrolase; EC

Butyryl cholinesterase catalyzes the hydrolysis of a number of choline esters as shown:

Acylcholine + H2O ---------> Choline + Corresponding Acid
The enzyme is sometimes referred to as ÒpseudocholinesteraseÓ but it preferentially uses butyrylcholine and benzoylcholine as substrates. Butyrylcholinesterase is distinct from acetylcholinesterase and is found in mammalian blood plasma, liver, pancreas, intestinal mucosa and the white matter of the central nervous system.

Butyrylcholinesterase from equine serum has a molecular weight of 440,000 (Lee, J.C. and Harpst, J.A., Biochemistry, 12, 1622, l973). It is a glycoprotein which has an optimum pH of 6.0-8.0. Assay of butyrylcholinesterase activity is of diagnostic value in various liver diseases, malignancies, and pulmonary tuberculosis (Methods of Enzymatic Analysis; Bergmeyer, H.U. ed: Vol. 2, 833, 1974. Academic Press, New York.) The enzyme can also be used for the assay of organophosphorous compounds such as pesticides.

The amount of enzyme causing the hydrolysis of one micromole of butyrylthiocholine iodide per minute at 25°C and pH 7.4.

  1. 0.05 M Tris-HCl buffer, pH 7.4.
  2. 0.25 mM 51,51-Dithiobis [2-nitrobenzoic aci] (DTNB) 0.1 mg/ml in 0.05 M Tris-HCl buffer, pH 7.4.
  3. 0.111 mM Butyrylthiocholine iodide (24 mg/ml in glass distilled water)
  4. Enzyme solution in 0.05 M Tris-HCl buffer, pH 7.4., to yield a concentration of 0.1 U/ml.

  1. Set spectrophotometer (equipped with strip chart recorder and temperature control) at 405 nm and 25°C.
  2. Into cuvettes, place the following reagents:
    DTNB 2.70 ml
    Butyrylthiocholine iodide 0.20 ml

    Mix and incubate in spectrophotometer for 5 min. and establish blank rate, if any.

  3. Initiate the reaction by adding 0.1 ml of the enzyme. Record the rate of absorbance at 405 nm for 5 min.
  4. Calculate (delta)E405 nm/min

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

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