-adrenergic receptor of the turkey erythrocyte. Molecular heterogeneity revealed by purification and photoaffinity labeling
The β1-adrenergic receptor of turkey erythrocytes has been purified by a combination of affinity and high performance steric exclusion chromatography. These procedures provide preparations with specific activities of > 15,000 pmol/mg of protein with an overall recovery of ~ 30% of the receptor activity solubilized from membrane preparations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radioiodinated purified receptor reveals two bands of labeled protein with apparent M(r) = 40,000 ± 2,000 and 45,000 ± 3,000 in a 3-4:1 ratio. These same two peptides can also be labeled specifically and in approximately the same ratio in both membranes and purified preparations using the photoaffinity probe 125I-labeled p-azidobenzylcarazolol. When the two purified polypeptides are completely separated by high performance liquid chromatography and subjected to detailed ligand binding studies, identical β1-adrenergic specificities are found for the two receptor forms. Preliminary characterization of these two proteins by partial protease digestion suggests a large degree if similarity between them, albeit with some significant differences. These results demonstrate that both purification and photoaffinity labeling identify two polypeptides in turkey erythrocyte membranes as containing a β1-adrenergic receptor binding site. The functional and structural relationships of these two forms of the receptor remain to be elucidated.
Shorr, RGL; Strohsacker, MW; Lavin, TN; Lefkowitz, RJ; Caron, MG
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