The purified receptor for calcium channel blockers (CaCB-receptor) from rabbit skeletal muscle contains three polypeptides within a molecular mass of 165, 55, and 32 kDa. cAMP-dependent protein kinase was shown to phosphorylate preferentially the 165-kDa protein. The major phosphorylation site was identified and compared with the recently published primary sequence of the CaCB-receptor. It is concluded that serine 687 is the phosphorylation site. Phosphorylation of serine 687 may regulate the open-state probability of the CaCB-receptor.
