Isolation and structural characterization of calcitonin gene-related peptide from the brain and intestine of the frog, Rana ridibunda

Calcitonin gene-related peptide (CGRP) was isolated in a single molecular form from an extract of the whole brain and from the small intestine of the European green frog, Rana ridibunda. The primary structure of the peptide was established as: Ala-Cys-Asn-Thr-Ala-Thr-Cys-Val-Thr- His¹⁰-Arg-Leu-Ala-Asp-Phe-Leu-Ser-Arg-Ser-Gly²⁰-Gly-Met-Ala-Lys-Asn-Asn-Phe-Val-Pro-Thr³⁰-Asn-Val-Gly-Ser-Lys-Ala-Phe-NH₂. Frog CGRP shows only two amino acid substitutions (Val²² → Met and Gly²³ å Ala) compared with chicken CGRP, as deduced from the nucleotide sequence of a cloned cDNA. The Asp¹⁴ residue, which leads to enhanced biological potency in chicken CGRP, is also present in the frog peptide. The data show that the structure of CGRP has been strongly conserved during evolution of the vertebrates.