Abstract
Complete separation of the [ 3H]ethylketocyclazocine ([ 3H]EKC) specific binding (k subtype) from tritiated Tyr-D-Ala 2-Me-Phe 4-Gly-ol 5 enkephalin (DAGO) and Tyr-D-Ala 2-L-Leu 5-enkephalin (DALA) binding (μ-and δ-subtypes, respectively) was achieved by Sepharose-6B chromatography and sucrose density gradient centrifugation of digitonin solubilized frog brain membranes. The apparent sedimentation coefficient ( S 20,w) for the k receptor-detergent complex was 13.1 S and the corresponding Stokes radius 64 Å. The isolated fractions exhibited high affinity for EKC and bremazocine, whereas μ- and δ-specific ligands were unable to compete for the [ 3H]EKC binding sites, indicating that the κ subtype represents a separate molecular entity from the μ and δ receptor sites.
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