ABSTRACT
Many lower vertebrates change body color in response to their background coloration by dispersing and concentrating melanin granules within the integumentary melanophores. It is now firmly established that the peptides are derived from a common precursor molecule, termed pro-opiomelanocortin (POMC) or pro-opiocortin. During the 1950s, two melanocyte-stimulating hormones (MSHs), α- and β-MSH, were identified in extracts from the posterior-intermediate lobes of mammalian pituitary glands. Although MSHs of amphibians have never been sequenced. MSHs of Xenopus laevis have been extensively characterized by Martens and Jenks. The elucidation of the entire base sequence of the cDNA coding for mammalian POMC revealed that they have repeating structural units of a common MSH core. Contribution of other parts of a-MSH to melanotropic activity has also been investigated by chain elongation of peptides, including the active site sequence. A tetrapeptide sequence, His-Phe-Arg-Trp, has been conserved within the structures of α-,β-, and γ-MSH, suggesting that this segment is essential for bioactivity.
