Isolation and structure of another hypothalamic peptide possessing MSH-release-inhibiting activity

Abstract A second peptide with the biological activity of an MSH-release-inhibiting factor (MIF) and with the amino acid composition His 1, Arg 1, Pro 1, Gly 1, Phe 1 was isolated from bovine hypothalami. This pentapeptide, when subjected to the combined Edman-dansyl degradation, yielded the sequence Pro-His-Phe-Arg-Gly-NH 2 , which was confirmed by derivatisation and mass spectral fragmentation. A peptide of similar structure was then synthesized. The chromagraphic and electrophoretic mobilities, biological activities, and mass spectral fragmentation patterns of the synthetic and natural peptides were compared and found to be similar. These studies suggest the existence of a hypothalamic pentapeptide, H-Pro-His-Phe-Arg-Gly-NH 2 , possessing MIF-activity.