A) Schematic representation of the human calcitonin receptor, a 7 pass transmembrane G-protein coupled receptor, with the 18 AA-long CRFP sequence from the intracellular C-terminal region shown in bold. B) Peptide sequences of the human, rat, and mouse CRFP homologues. The sequences are highly conserved and deviations from the human sequence are indicated in bold. C) Amidation reaction required to stabilize and induce biological activity of CRFP, enzymes (in italics) sequentially modify the indicated residues (in bold) to yield the mature 12 AA-long pyroglutimated and amidated CRFP.