Spectral study of the peripheral site of ligand binding in the active center of cholinesterases from different natural sources

An increased ethidium bromide fluorescence at 610 nm was observed in the presence of cholinesterases from some natural sources, and a new fluorescence band appeared in the 500–570 nm region. The data obtained suggest a resonance energy transfer from the cholinesterase-ethidium bromide complex to a free ethidium bromide molecule. The structure of the peripheral ligand binding sites in the active center of bovine erythrocyte acetylcholinesterase, horse serum butyrylcholinesterase, and squid ganglia propionylcholinesterase proved essentially similar.