Acetylcholinesterase of Mammalian Neuromuscular Junctions: Presence of Tailed Asymmetric Acetylcholinesterase in Synaptic Basal Lamina and Sarcolemma

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 80; no. 21; pp. 6698 - 6702
• Main Authors: Dreyfus, Patrick A., Rieger, François, Pinçon-Raymond, Martine
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 01.11.1983; National Acad Sciences
• Subjects: acetylcholinesterase; Acetylcholinesterase - metabolism; Animals; Basement membrane; Basement Membrane - enzymology; Cell membranes; Centrifugation; Detergents; Extracellular matrix; Extracellular Matrix - enzymology; Fractionation; Macromolecular Substances; Matrix materials; Mice; microsomes; Motor Endplate - enzymology; Neuromuscular Junction - enzymology; neuromuscular junctions; Salts; Sarcolemma - enzymology; Solubility; Solubilization; Subcellular fractions
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.80.21.6698

A sarcolemma-rich fraction can be isolated after subcellular fractionation of mouse intercostal muscles by sedimentation on a discontinuous sucrose gradient. The quantitative recovery of the acetylcholine receptor in this fraction is about 50%, which indicates the presence of a high proportion of postsynaptic membranes. Acetylcholinesterase (AcChoEase; EC 3.1.1.7) is found mainly in three different layers: the top layer, which contains soluble AcChoEase, the intermediate layer (fraction A), and the last, AcChoR-rich, layer (fraction C). The relative proportions of the molecular forms of AcChoEase are different in the three layers. The ``16S'' AcChoEase is in a higher proportion in both types of membrane fractions (A and C) compared to soluble AcChoEase. Both total AcChoEase and 16S AcChoEase are enriched in the A and C fractions. In the C fraction, the sequential use of homogenizations in the presence of detergent and high ionic strength allows the ``solubilization'' of two distinct AcChoEase pools. One is detergent-soluble and mainly composed of slow-sedimenting forms; the other one is detergent-insoluble, high-ionic strength-soluble, and composed mainly of collagen-like, tailed, asymmetric (16S) AcChoEase. Thus, most of the asymmetric AcChoEase is specifically localized in the synaptic extracellular matrix of the mammalian muscle fiber. However, in the A fraction, most of the 16S AcChoEase found is solubilized by detergent alone, suggesting an association with microsomal membranes. It may mean that at least some of the basal lamina-embedded 16S AcChoEase is preassembled intracellularly in the sarcoplasmic reticulum.