New enzymatic assay of cholinesterase activity

A new enzymatic method for the determination of serum pseudo-cholinesterase activity is described. Choline, which is liberated from benzoylcholine as substrate by cholinesterase, is oxidized by choline oxidase to betaine with the simultaneous production of hydrogen peroxide, which oxidatively couples with 4-aminoantipyrine and phenol in the presence of peroxidase to yield a chromogen with maximal absorbance at 500 nm. The calibration curve is linear up to 1500 units per liter of serum. The method is reproducible, and the results correlate well with those obtained by the method using butyrylthiocholine as substrate and 5,5'-dithiobis-(2-nitrobenzoic acid) as color reagent.