Mammalian .beta.2-adrenergic receptor: purification and characterization

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Abstract
The .beta.2-adrenergic receptors from hamster, guinea pig and rat lungs were solubilized with digitonin, and were purified by sequential Sepharose-alprenolol affinty and high-performance steric-exclusion liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography of iodinated purified receptor preparations reveal a peptide with an apparent MW of 64,000, in all 3 systems, that coincides with the peptide labeled by the specific .beta.-adrenergic photoaffinity probe (p-azido-m-[125I]iodobenzyl)carazolol. A single polypeptide was observed in all 3 systems, suggesting that lower MW peptides, identified previously by affinity labeling or purification, in mammalian systems may represent proteolyzed forms of the receptor. Purification of the .beta.-adrenergic receptor was also assessed by silver staining, iodinated lectin binding and measurement of the specific activity (.apprx. 15,000 pmol of [3H]dihydroalprenolol bound/mg of protein). Overall yields approximate 10% of the initial crude particulate binding, with 1-3 pmol of purified receptor obtained/g of tissue. The purified receptor preparations bind agonist and antagonist ligands with the expected .beta.2-adrenergic specificity and stereoselectivity. Peptide mapping and lectin binding studies of the hamster, guinea pig and rat lung .beta.2-adrenergic receptors reveal significant similarities, suggestive of evolutionary homology.