The biochemical characterization of the pro-opiomelanocortin (POMC) products, isolated and purified from a human anterior lobe pituitary adenoma associated with Cushing's Syndrome, illustrates the processing of this prohormone. In the tumor, 87% of the acidic joining peptide (AJP) is found as a dimer rather than as a monomer, the prevalent form found in normal pituitary tissue. The corticotropin (ACTH) purified and characterized from the tumor was found not to be phosphorylated. In contrast, human ACTH of normal pituitary origin is found to be 30% phosphorylated at the serine residue at position 31. No evidence of cleavage at residues 49-50 to produce $ tau sb3$-MSH and the 1-49 fragment was found. / ACTH was purified from extracts of guinea-pig anterior pituitaries and characterized in terms of its amino acid composition and molecular weight using IS-MS and HPLC. Guinea-pig ACTH was found to have a similar activity to that of human ACTH with respect to the maximal steroid output of corticosterone and aldosterone. However, it proved to be slightly more potent in terms of the concentration which elicited half-maximal steroid secretion. Under the assay conditions used, guinea-pig ACTH does not seem to a superagonist as suggested by a previous study. Combining amino acid compositions, mass spectrometric data, and the recent determination of the cDNA sequence for guinea-pig ACTH, the identification of various purified biosynthetic derivatives of guinea-pig POMC was facilitated. / Joining peptide, a major product of POMC processing, was found in extracts of both anterior and neurointermediate lobes. The purified peptide corresponded exactly in amino acid composition and mass to the predicted structure established by the CDNA sequence. Also, by using ion-spray mass spectrometry, post-translational modifications of other products of intermediate lobe processing were observed. N- and O-acetylation of $ alpha$-melanotrophin, partial O-phosphorylation of corticotrophin-like intermediate lobe peptide and carboxyl-terminal amidation of $ beta$-melanotrophin were identified. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.22795 |
| Date | January 1994 |
| Creators | Robinson, Patrick, 1964- |
| Contributors | Bennett, Hugh (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001440873, proquestno: MM05619, Theses scanned by UMI/ProQuest. |
Page generated in 0.0032 seconds