BUTYRYLCHOLINESTERASE ACTIVITY TOWARDS LONG-CHAIN ALKANOYLCHOLINES - KINETICS AND MECHANISM

The hydrolysis of long-chain alkanoylcholines catalyzed by butyrylchol inesterase (EC 3.1.1.8) has been studied. Radiolabelled substrates hav e been used and a radiochromatographic detection method developed earl ier has been applied. The long-chain choline esters were found to be e xcellent substrates for butyrylcholinesterase at low concentrations, w ith K(m) values lower than those of short-chain analogues. At higher s ubstrate concentrations, however, the hydrolysis reaction is inhibited , due to the formation of mixed micelles between the amphiphilic subst rate and the corresponding alkanoic acid formed in the hydrolysis reac tion. The inhibition may also partially be the result of conformationa l changes of the protein following adsorption of the cationic amphiphi le. Critical micelle concentrations (CMC) for the long-chain substrate s, as well as for mixed micelles, have been determined.