Primary structure and bioactivity of bullfrog calcitonin

Calcitonin was isolated from the bullfrog, Rana catesbeiana, and the first amino acid sequence of an amphibian calcitonin was determined to be Cys-Ser-Gly-Leu-Ser-Thr-Cys-Ala-Leu-Met-Lys-Leu-Ser-Gln-Asp-Leu-His- Arg-Phe-Asn-Ser-Tyr-Pro-Arg-Thr-Asn-Val-Gly-Ala-Gly-Thr-Pro-NH2. Some portions of this sequence are specific to bullfrog calcitonin, and other portions are similar both to teleost calcitonins and to mammalian calcitonins. Administration of 5 pmol of bullfrog calcitonin to rats revealed a hypocalcemic potency similar to that of salmon calcitonin, at least for the first 3 hr.