Isolation and characterization of corticotropin- and melanotropin-related peptides from the neurointermediary lobe of the rat pituitary by reversed-phase liquid chromatography.

A novel procedure utilizing reversed-phase high-performance liquid chromatography for the extraction and purification of peptides from biological tissues has been applied to the isolation of corticotropin-like intermediary lobe peptide (CLIP) and alpha-melanocyte-stimulating hormone (alpha-MSH) from the neurointermediary lobe of the rat pituitary. The isolation and characterization of two major forms of CLIP and two major forms of alpha-MSH are described. The isolated peptides have been identified by using enzymatic digestions and peptide mapping. The main form of ClIP is a peptide which has been modified by phosphorylation of the serine residue at position 31. This is the first peptide of endocrine origin reported to be modified in such a manner. A non-phosphorylated form of CLIP was also present at lower concentrations. The main form of alpha-MSH was found to be N,-O-diacetyl-alpha-MSH, with the more familiar mono-N-acetyl-alpha-MSH present to a much smaller extent. Thus, in the rat neurointermediary lobe, the two main corticotropin-related peptides present are mostly in modified forms which are the result of posttranslational modifications. It is only by the use of methodology such as that described in this paper that small alterations in peptide structure may be identified.