Molecular Structure and Catalytic Activity of Membrane-Bound Acetylcholinesterase from Electric Organ Tissue of the Electric Eel

The catalytic activity of membrane-bound acetylcholinesterase in electric organ tissue was shown to be governed by diffusion- controlled substrate and hydrogen ion gradients, generated by acetylcholinesterase-catalysed hydrolysis leading to a lower substrate concentration and pH in the vicinity of the particulate enzyme. Various solubilization procedures, including extraction with salts and detergents, chemical modification proteolysis showed that interaction of most of the acetylcholinesterase with the excitable membrane is primarily electrostatic, but that part of the enzyme seems to be more intimately associated with the membrane. \u27Native\u27 acetylcholinesterase, as isolated from fresh electric organ tissue, is a complex molecular structure in which a multisubunit head is connected to an elongated tail. Proteolytic digestion or autolysis leads to detachment of the tail and conversion of acetylcholinesterase to a globular tetramer containing four similar subunits in which each pair is connected by disulfide bonds. Further digestion leads to cleavage of the individual polypeptide chains of the subunits which are not, however, released unless the enzyme is denatured. The possible modes of attachment of the \u27native\u27 acetylcholinesterase molecule to the excitable membrane are discussed