Cocaine and butyrylcholinesterase (BChE): determination of enzymatic parameters

In humans, the plasma enzyme, butyrylcholinesterase (E.C. 3.1.1.8), metabolizes cocaine to the water-soluble, pharmacologically inactive compounds, ecgonine methylester and benzoic acid. Homogeneous enzyme was purified from human plasma and used to determine the enzyme kinetic parameters of Km and Vmax with cocaine as the substrate. The KM (11.9 microM) indicates that cocaine is tightly bound to the four active sites of the native tetramer. The Vmax (1.17 microM/min) is 50-fold greater than cocaine catalytic antibodies. Administration of purified human butyrylcholinesterase to a cocaine-intoxicated patient would be expected to shift the metabolism to the inactive metabolites and reduce the toxicity.