ISOLATION AND CHARACTERIZATION OF MELANOTROPINS FROM LAMPREY PITUITARY-GLANDS

Three peptides containing the melanotropin-core amino-acid sequence, Y XMXHFRWG, were isolated from the pituitary glands of a modern represen tative of the most primitive vertebrates, the sea lamprey, Petromyzon marinus. MSH-A, a nonadecapeptide (NPELYQMNHFRWGQPPTHF), is free at bo th ends. MSH-B, an eicosapeptide (VQESADGYRMQHFRWGQPLP), is free at th e N-terminus and amidated at the C-terminus. They differ strikingly fr om gnathostome MSHs in structure. The third peptide, with an apparent molecular weight of 15 kDa, was tentatively designated lamprey ACTH, b ased on a structural feature: the N-terminal 22-residue-MSH (SVSSPKYAM GHFRWGSPDKATI) is Followed by four consecutive basic amino acids (RKRR ) and a ACTH-like sequence (PVRPNTSDSPEIPDYAF-). MSH-B is 10 and 100 t imes more potent than a-MSH and MSH-A, respectively, in a frog skin as say in vitro, whereas the lamprey ACTH showed no melanotropic activity , Lamprey ACTH did, however, show corticotropic activity on the lampre y pronephric and mesonephric tissue. (C) Munksgaard 1995.