“Joining peptide” of pro-opiomelanocortin. II. Interspecies heterogeneity of the joining peptide fragment

Abstract

The use of an antiserum raised against the joining peptide sequence −23 to −14 of bovine pro-opiomelanocortin (POMC) enabled the detection of related immunoreactive sequences of peptides in bovine, porcine, mouse and guinea-pig pituitaries, as well as in mouse brain and cerebral cortex, guinea-pig cerebral cortex, and bovine hypothalamus. Gel chromatography of pituitary extracts (Sephadex G-75 and Bio-Gel P-4) indicated the presence of several immunoreactive joining peptide fragments ranging in the molecular weight range (Mr) of 1,500 to 2,300. Furthermore, high molecular weight ( Mr>22,500 ) immunoreactive-precursor from bovine anterior pituitary was readily digested with trypsin into an immunoreactive fragment of approximately Mr 1,500. Analyses of these immunoreactive peptides by reverse-phase high-performance liquid chromatography (HPLC) led to their resolution into six distinct peptides. The only apparent correspondence in the elution profiles of immunoreactive peptide profiles between different mammalian species was the identification of a similar fragment (Mr 2,000) from bovine and guinea-pig pituitaries. Thus, we conclude that immunoreactivity to the joining peptide region of POMC from various mammalian species exhibits a degree of heterogeneity in its composition. The relatively low levels of immunoreactivity in comparison to that of ACTH also suggest that the joining peptide domain may be further processed. The hormonal status of the joining peptide region remains to be determined.