Abstract
Our previous study demonstrated that both the method of serum cholinesterase activity measurement proposed in the draft of the Japan Society for Clinical Chemistry (JSCC) and the European Committee for Clinical Laboratory Standards (ECCLS) reference method showed residual activity after inhibition by tetraisopropyl pyrophosphoramide (TIPA), and this residual activity appeared to be related to the concentration of human serum albumin (HSA). By replacing 2, 3-dimethoxybenzoylthiocholine iodide (DMBT) with benzoylthiocholine iodide as a substrate in the reagent composition JSCC proposed method, no residual activity after TIPA inhibition was observed. In protein denaturation testing by sodium dodecylsulfate addition to the reagents, the residual activity of inhibition by TIPA was not changed. Based on these observations, the existance of residual activity obseved in the JSCC proposed method appeared to be caused by the non-enzymatic hydrosis of DMBT by albumin. To detect thiocholine, it was demonstrated that the molecular extinction coefficient of 5-thio-2-nitrobenzoate, which was obtained from 5, 5'-dithiobis (2-nitrobenzoate), fluctuated according to the HSA concentration, whereas 2-thiopyridone, which was obtained from 2, 2'-dipyridildisulfide, was not likely influenced. With the ECCLS reference method, no sufficient measuring range was obtained, so the issue of proportional quantity remains unclear.
