Fragments of mouse diaphragm and sternomastoid muscles were incubated in diisopropyl-fluorophosphate (DFP)-3H in conditions known to saturate all the available DFP-sensitive reaction sites. After being extensively washed, the enzyme acetylcholinesterase (AChase) was specifically reactivated by treatment with pyridine-2-aldoxime methiodide (2-PAM). The radioactive DP-groups released into solution by 2-PAM were measured by liquid scintillation counting, and related to the known number of motor endplates present. Considerable difficulty was encountered in reducing the excess, adsorbed radioactivity to acceptable levels: long washing routines, extraction with organic solvents, and removing excess muscle fiber by microdissection were necessary. Six experiments gave a mean value of 2.4 x 107molecules AChase per sternomastoid endplate, in reasonable agreement with the previously reported measurements by radioautography.
QUANTITATIVE STUDIES ON ENZYMES IN STRUCTURES IN STRIATED MUSCLES BY LABELED INHIBITOR METHODS : II. Confirmation of Radioautographic Measurement by Liquid-Scintillation Counting
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A. W. Rogers, E. A. Barnard; QUANTITATIVE STUDIES ON ENZYMES IN STRUCTURES IN STRIATED MUSCLES BY LABELED INHIBITOR METHODS : II. Confirmation of Radioautographic Measurement by Liquid-Scintillation Counting . J Cell Biol 1 June 1969; 41 (3): 686–695. doi: https://doi.org/10.1083/jcb.41.3.686
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