Identification and Ligand-Induced Modification of the cAMP Receptor in Dictyostelium

Photoaffinity labeling with 8-N₃[³²P]cAMP and in vivo phosphorylation with ³²PO₄ provide sensitive methods for the identification of the surface cAMP receptor. Photoaffinity labeling achieves high specificity while in practice, the in vivo³²P labeling affords considerably higher sensitivity. Both methods allow fairly direct assays of cellular responses to an extracellular cAMP stimulus at the level of the receptor—a shift in electrophoretic mobility and a rise in phosphorylation. Quantification of the shift in mobility, assayed by photolabeling, has shown a strong correlation between modification of the receptor and adaptation. These labelling techniques will also help to elucidate the role of the concomidant changes in receptor phosphorylation, which may cause the change in electrophoretic mobility. Furthermore, photolabeling and ³²P labeling will allow study of the possible multiple affinity classes of the cAMP receptor and of the possible expression of cAMP receptors in later stages of development.