Asymmetry of Acetylcholinesterase and Acetylcholine Receptor in Intact Secretory Vesicles from Adrenal Medulla

Abstract

Abstract Highly purified secretory vesicles from adrenal medulla, isolated by differential and density gradient centrifugation using isotonic gradient material (Percoll™), contain acetylcholinesterase. The enzyme was latent in isolated secretory vesicles i.e. acetylcholinesterase was inaccessible to added substrate. The enzyme activity became patent after addition of detergent or in hypotonic media. Hypotonic treatment or specific lysis of the vesicles with Mg 2+ /ATP in the presence of a permeant anion resulted in the release of soluble acetylcholinesterase from the vesicular content. Membrane-bound enzyme sedimented with the membranes. Binding of α-bungarotoxin could only be observed when secretory vesicles were lyzed. It is concluded, that the acetylcholine receptor as well as the membrane-bound form a acetylcholinesterase are localized on the inner surface of the secretory vesicle membrane, which becomes the outer surface of the cell membrane during exocytosis. Concomitantly the soluble form of acetylcholinesterase present within secretory vesicles is released into the extracellular fluid.