Phosphinate inhibition studies of cholinesterases

The kinetic constants, K_d, k₂, and k_i, were determined for the inhibition by 4-nitro-phenyl methyl(phenyl)phosphinate of three cholinesterases: butyrylcholinesterase, bovine erythrocyte acetylcholinesterase and eel acetylcholinesterase. Stopped-flow kinetic evaluations and automated data acquisition and processing were employed. A broad range in affinity for the phosphinate inhibitor was observed as reflected by the binding constants, K_d. A similar wide range in the k₂ values for the unimolecular inhibition step was obtained. The net bimolecular rate constants, ki, indicate equal overall reactivity for butyrylcholinesterase and eel acetylcholinesterase with a smaller inhibition rate constant for bovine erythrocyte acetylcholinesterase.