Natural occurrence but lack of melanotrophic activity of gamma-MSH in fish
McLean, C.; Lowry, P.J.
Nature 290(5804): 341-343
1981
ISSN/ISBN: 0028-0836 PMID: 7207629 Document Number: 174613
When adrenocorticotropin (ACTH) and β-lipotropin (LPH) are enzymatically cleaved in the pituitary from their common precursor molecule, a glycopeptide with an apparent molecular weight of 16,000 remains (reviewed in ref. 1). Sequencing of a c Dna copy of the bovine pituitary m Rna for the precursor molecule demonstrated that, within the region encoding the 16,000-mo Iecular weight (MW) glycopeptide, there was a short sequence homologous with the α-melanocyte-stimulating hormone (α-MSH) contained in Acth and the β-Msh within β-LPH2. It was therefore proposed that the region of homology coded for a γ-Msh which might have biological activity, although synthetic peptides containing this sequence were shown to have poor melanotrophic activity3. In the pars intermedia further rapid enzyme modification converts Acth to α-Msh and corticotropin-like intermediate lobe peptide (CLIP), and β-Lph to β-Msh and β-endorphin. Although smaller peptides containing the γ-Msh structure have been detected in extracts of the bovine pars intermedia4,5, the major post-translational products of the 16,000-Mw fragment are present mainly as large glycosylated peptides1,4. We report here that a major peptide product of the neurointermediate lobe of the dogfish pituitary which we had previously shown to lack melanotrophic activity has a γ-MSH-like structure. Therefore if γ-Msh is a peptide with a function it is not one shared with the melanotrophic hormones.