Sucrose density gradient centrifugation of digitonin-solubilized opioid binding sites from guinea pig brain and cerebellum was carried out. Centrifugation of extracts of whole brain into a gradient devoid of sodium and low in digitonin revealed the presence of two well-separated peaks of opioid binding activity. Peak A was shown to have the binding characteristics of κ sites, whereas peak B seems to be a mixture of μ and δ sites. When extracts of guinea pig cerebellum were treated in the same manner, a single peak of binding activity was obtained that coincided with peak A from guinea pig brain and exhibited the characteristics of κ binding sites. All three sites closely resemble their membrane-bound counterparts, retaining good affinity and selectivity for their appropriate ligands. The apparent sedimentation coefficients (S20,Ω) of the digitonin-solubilized binding sites present in the two peaks are 19 s for peak A and 34-39 s for peak B, and the estimated apparent molecular weights are 400,000 for κ sites and 750,000-875,000 for the mixture of μ and δ sites. Our results suggest that κ sites constitute separate molecular entities from μ and δ sites.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Issue number||13 I|
|State||Published - 1984|
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