Procedure for Detecting Atypical Serum Cholinesterase Using o-Nitrophenylbutyrate as Substrate

A method has been developed for demonstrating atypical serum cholinesterase by means of the self-indicating substrate, o-nitrophenylbutyrate and the inhibitor suc-cinyldicholine. The procedure was tested for atypical cholinesterase with 76 indi-viduals, including 5 otherwise proven homozygotes and their immediate families. In all cases, it was possible to distinguish clearly those individuals homozygous for the usual and atypical cholinesterase as well as heterozygotes. CERTAIN INDIVIJALS are genetically homozygous for a form of serum cholinesterase which has been designated as atypical (1, 2).t Following administration of the muscle relaxant, succinyldicholine (SDC), these people exhibit prolonged apnea due to a decreased rate of destruction of this drug by their atypical serum cholinesterase. The most widely used technic for detecting these individuals is the dibucaine number procedure of Kalow (2, 3). This method is precise, unequivocal, and simple, hut requires a good spectrophotometer capable of accurately measuring absorbance changes in the far ultraviolet ill the presemice of a high background absorbance due to serum. Ami alteriiate to the dibu-caine number procedure is described below. This method makes use of the cholinesterase substrate o-nitrophenylbutyrate (NPB) and tile hi-hibitor succinyldicholine (SDC). In addition, results are presented which indicate differences in reactivity of choline and noncholine sub-strates to the usual and atypical forms of the enzyme