[A study of the peripheral quaternary ligand binding site of cholinesterase with the use of ethidium bromide].

The peripheral binding site of horse serum cholinesterase (EC 3.1.1.7) for quaternary ligands was investigated by fluorescent probing with the use of ethidium bromide. Spectral evidence for the participation of the tryptophan indole group of the peripheral site of horse serum cholinesterase in the formation of a cholinesterase complex with ethidium bromide is presented. The mechanism of cholinesterase effect on ethidium bromide fluorescence is proposed.