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Oligomeric Structure of Muscarinic Receptors is Shown by Photoaffinity Labeling: Subunit Assembly May Explain High- and Low-Affinity Agonist States

Sofia Avissar, Gabriel Amitai and Mordechai Sokolovsky
Proceedings of the National Academy of Sciences of the United States of America
Vol. 80, No. 1, [Part 1: Biological Sciences] (Jan. 1, 1983), pp. 156-159
Stable URL: http://www.jstor.org/stable/13340
Page Count: 4
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Oligomeric Structure of Muscarinic Receptors is Shown by Photoaffinity Labeling: Subunit Assembly May Explain High- and Low-Affinity Agonist States
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Abstract

The potent muscarinic photoaffinity reagent N-methyl-4-piperidyl p-azidobenzilate (azido-4NMPB) was used to covalently label specific muscarinic binding sites in various brain regions and in the heart. In the cortex and hippocampus, a single specifically labeled protein with an apparent molecular mass of 86,000 daltons was detected by gel electrophoresis. In the medulla pons, cerebellum, and cardiac atria, there was a 160,000-dalton band in addition to the 86,000-dalton polypeptide. Under certain conditions, alkali or hydroxylamine treatment dissociated both macromolecules into a single 40,000-dalton polypeptide. These results suggest that the muscarinic receptor exists in oligomeric forms and that a dimer and tetramer of a basic 40,000-dalton peptide may exist as interconvertible species. We propose a model to explain the biological architecture of the muscarinic receptors and suggest a possible correlation between the azido-4NMPB-labeled polypeptides and the two states of the receptor observed in agonist binding experiments.

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