Purified rat hepatic β₂-adrenergic receptor. Structural similarities to the rat fat cell β₁-adrenergic receptor

The mammalian β₂-adrenergic receptor from rat liver has been purified by sequential cycles of affinity chromatography followed by steric exclusion high performance liquid chromatography. In purified preparations, the overall yield of receptor approaches 10%. Sodium dodecyl sulfate-polyacrylamide gel-electrophoresis of highly purified receptor preparations reveals a single peptide, M(r) = 67,000, as judged by silver staining. Purified β₂-adrenergic receptor migrates on the steric-exclusion high performance liquid chromatography in two peaks, M(r) = 140,000 and 67,000. Specific binding of (-)-[³H]dihydroalprenolol and (-)-[¹²⁵I]iodocyanopindolol to purified rat liver β-adrenergic receptor preparations is stereoselective and displays a rank order of potencies characteristic of a β₂-adrenergic receptor. The mammalian β₁-adrenergic receptor of rat fat cells has also been purified (Cubero, A., and Malbon, C.C. (1984) J. Biol. Chem. 259, 1344-1350). When purified in the presence of protease inhibitors, radioiodinated β₁-adrenergic receptors from rat fat cells and β₂-adrenergic receptors from rat liver comigrate on sodium dodecyl sulfate-polyacrylamide gels as 67,000 M(r) peptides. Autoradiograms of two-dimensional partial proteolytic digests of the purified, radioiodinated rat liver β-adrenergic receptor, as generated by α-chymotrypsin, Staphylococcus aureus V8 protease, and elastase reveal a pattern of peptide fragments essentially identical to those generated by partial proteolytic digests of the purified radioiodinated β₁-receptor from rat fat cells. This data suggests that a high degree of homology exists between these two pharmacologically distinct mammalian β-adrenergic receptor proteins.