A Rapid and Simple Ultramicromethod for the Estimation of Serum Pseudocholinesterase with Butyrylthiocholine as Substrate

　A simple and rapid ultramicromethod for the determination of serum pseudocholinesterase with butyrylthiocholine as substrate was devised. Its principle consists in reading the initial velocity of the reaction of DTNB with thiocholine which is enzymatically released from butyrylthiocholine at 37 ℃. The production rate of the chromogenic substance (5-mercapto-2-nitrobenzoic acid), namely the time (in seconds) necessary for causing an increment of 0.10 in absorbance is measured at 410 mμ, in a photoelectric colorimeter equipped with a cuvette holder and a drain system warmed at constant temperature (37℃). The method is suitable not only routine clinical chemistry but also for emergency clinic. It requires minimal equipment, specimens, pipetting and time, but has satisfactory precision and accuracy.