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* Department of Cell Biology and Anatomy, University of Miami School of Medicine, Miami, Florida, and The highly organized pattern of acetylcholinesterase (AChE) molecules attached to the basal
lamina of the neuromuscular junction (NMJ) suggests
the existence of specific binding sites for their precise
localization. To test this hypothesis we immunoaffinity purified quail globular and collagen-tailed AChE forms
and determined their ability to attach to frog NMJs
which had been pretreated with high-salt detergent
buffers. The NMJs were visualized by labeling acetylcholine receptors (AChRs) with TRITC-
Department of
Anatomy and Cell Biology, Hebrew University-Hadassah Medical School, Jerusalem, Israel
-bungarotoxin and AChE by indirect immunofluorescence; there
was excellent correspondence (>97%) between the distribution of frog AChRs and AChE. Binding of the
exogenous quail AChE was determined using a speciesspecific monoclonal antibody. When frog neuromuscular junctions were incubated with the globular G4/G2
quail AChE forms, there was no detectable binding
above background levels, whereas when similar preparations were incubated with the collagen-tailed A12
AChE form >80% of the frog synaptic sites were also
immunolabeled for quail AChE attached. Binding of
the A12 quail AChE was blocked by heparin, yet could
not be removed with high salt buffer containing detergent once attached. Similar results were obtained using
empty myofiber basal lamina sheaths produced by mechanical or freeze-thaw damage. These experiments
show that specific binding sites exist for collagen-tailed AChE molecules on the synaptic basal lamina of the
vertebrate NMJ and suggest that these binding sites
comprise a "molecular parking lot" in which the AChE
molecules can be released, retained, and turned over.
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