Cholinesterase (CHE) catalyzes the hydrolysis of the substrate butyrylthiocholine, forming butyrate and thiocholine. The latter reduces 5,5'-mercaptobis-2-nitrobenzoic acid (DMNB) to 5-mercapto-2-nitrobenzoate (5-MNBA), a colored compound. The reaction is kinetically monitored at 405 nm based on the rate of yellow color formation, proportional to CHE activity in the sample.
