A COMPARISON OF OPTICAL AND MANOMETRIC METHODS FOR THE ASSAY OF HUMAN SERUM CHOLINESTERASE

Abstract

A method for the assay of human serum cholinesterase (pseudocholinesterase) is described in detail. The disappearance of benzoylcholine is measured by ultraviolet spectrophotometry. Minute amounts of serum and of the substrate are sufficient for a rapid and convenient test of good accuracy. The influence of temperature on the reaction rate is given particular attention, since temperature control is not as easily achieved in the spectrophotometer as for instance in a Warburg apparatus. Although the results of the spectrophotometric assay are fundamentally the same as those obtained by using a conventional gasometric method with acetylcholine as a substrate, small but significant differences between the two answers occur. These differences depend on the substrates and not on the methods as such. The ratio of hydrolysis rates of the two substrates, benzoylcholine and acetylcholine, varies slightly from person to person. If benzoylcholine is used in the Warburg apparatus, a concentration above the optimum must be employed in order to develop sufficient gas for measurement.