Photoaffinity labeling of turkey erythrocyte beta-adrenergic receptors: degradation of the Mr = 49,000 protein explains apparent heterogeneity.

The potent photoaffinity probe [125I]p-azidobenzylcarazolol was used to identify beta-adrenergic receptors from turkey erythrocytes. Two peptides were specifically labeled with apparent Mr = 39,000 and 49,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The ratio of labeling of these peptides was found to be dependent on the method of tissue preparation. Thus, the Mr = 39,000/Mr = 49,000 ratio was 1:2 when labeling was done on intact cells, 1:1 for labeling of crude membranes, and 4:1 for purified membrane preparations. Moreover, incubation of intact cells or either membrane preparation at 37 degrees C led to a diminution of the Mr = 49,000 labeled peptide which was associated with a stoichiometric increase in the Mr = 39,000 form of the receptor. These results suggest that the turkey erythrocyte beta-adrenergic receptor is a protein of Mr = 49,000 and that the commonly observed Mr = 39,000 peptide is derived from this protein.