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Characterization of Opioid Receptor Subtypes in Solution
Author(s) -
DemoliouMason Catherine D.,
Barnard Eric A.
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb00627.x
Subject(s) - chemistry , dynorphin , cooperative binding , receptor , digitonin , enkephalin , opioid receptor , cooperativity , stereochemistry , binding site , opioid peptide , ligand (biochemistry) , biophysics , biochemistry , membrane , opioid , biology
Stable opioid receptor binding activity that retains distinct subtype specificities (μ, 6, and K) has been obtained in high yields in digitonin extracts of rat brain membranes that had been preincubated with Mg 2+ prior to solubilization. The dependence on Mg 2+ ions for receptor activity is also expressed in the soluble state, where the presence of Mg 2+ leads to high‐affinity and high‐capacity opioid peptide binding to the δ, μ, and K sites (the latter subtype measured by the binding of [ 3 H]dynorphin 1–8 ). Binding of opiate alkaloids to soluble receptor sites is less dependent on Mg 2+ than is opioid peptide binding. Soluble opioid binding activity shows the same sensitivity to Na + ions and guanine nucleotides as the membrane‐bound receptor. The ligand‐receptor interactions give evidence of strong positive cooperativity, which is interpreted in terms of association‐dissociation of receptor subunits on ligand binding in solution. Binding of enkephalin peptides is associated with the large macromolecules present (apparent Stokes radii > 60 Å), whereas both those and several small species present (< 60 Å) bind opiate alkaloids and dynorphin 1–8 .