Abstract
Recent work in several laboratories has proven that ACTH, LPH-endorphin, and another peptide of 103 amino acids (the N-terminal fragment) all derive from a single polypeptide, pro-opiocortin. Recently we showed that the pro-opiocortin produced by a pituitary tumor from a patient with Nelson syndrome was indistinguishable from the pro-opiocortin produced by an ectopic ACTH-producing tumor, suggesting both eutopic and ectopic ACTH arise from the same gene (Proc. Natl. Acad. Sci. 77: 5211, 1980). We have now analyzed tissue from a tumor producing Cushing disease. Two-dimensional (2-D) gel electrophoresis of proteins synthesized and labeled in vitro with [35S] methionine and [3H] glucosamine indicates that pro-opiocortin is processed by the same scheme in Cushing tumors as in Nelson tumors and mouse AtT-20 cells. The 35 kilodalton pro-opiocortin is first glycosylated, then the βLPH moiety is cleaved off, followed by cleavage of the ACTH moiety, leaving the glycosylated N-terminal fragment. No further cleavage of the N-terminal fragment was detected. Electrophoresis of tryptic peptides of pro-opiocortin labeled with [35S] methionine and [3H] glucosamine confirms the conclusion from the 2-D gels that the single glycosylation site of human pro-opiocortin lies in the N-terminal fragment.
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Miller, W., Johnson, L. Processing of pro-opiocortin in Cushing tumors. Pediatr Res 15, 1539 (1981). https://doi.org/10.1203/00006450-198112000-00025
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DOI: https://doi.org/10.1203/00006450-198112000-00025