Isolation and Amino Acid Sequence of Corticotropin-Releasing Factor from Pig Hypothalami

A polypeptide was isolated from acid extracts of porcine hypothalami on the basis of its high ability to stimulate the release of corticotropin from superfused rat pituitary cells. After an initial separation by gel filtration on Sephadex G-25, further purification was carried out by reversed-phase HPLC. The isolated material was homogeneous chromatographically and by N-terminal sequencing. Based on automated gas-phase sequencing of the intact and CNBr-cleaved peptide and on carboxypeptidase Y digestion, the primary structure of this 41-residue polypeptide was determined to be Ser-Glu-Glu-Pro-Pro-Ile-Ser-Leu_Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu-Val-Leu-Glu-Met-Ala-Arg-Ala-Glu-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn-Arg-Lys-Leu-Met-Glu-Asn-Phe-NH2. Porcine corticotropin-releasing factor (CRF) shares a common amino acid sequence (residues 1-39) with rat and human CRF and differs from these only in positions 40 and 41. However, isoleucine was also present at position 40 in porcine CRF, but in a smaller percentage than asparagine. The sequence of porcine CRF shows 83% homology with ovine CRF. Porcine CRF markedly stimulated the release of corticotropin from superfused rat and pig pituitary cells. The biological activity and close structural relationship to CRFs of other species indicate that the peptide isolated represents porcine CRF.