The common prohormone of corticotropin and the opiate peptide lipotropin C-fragment (beta-endorphin)

Chemistry and biosynthesis of pro-opiomelanocortin. ACTH, MSH's, endorphins and their related peptides

Studies of lipotropins, melanotropins and endorphins on one hand, and of adrenocorticotropin on the other, has given rise to the concept of a multipotent precursor molecule recently renamed proopiomelanocortin. The preferential sites of cleavage of the precursor to produce its biologically active components are made of pairs of basic amino acid residues as described for the biosynthesis of beta-MSH and pro-insulin. Such structural feature is also found in other pro-hormone molecules. Pulse chase experiments and secretory studies carried out in both anterior and intermediate lobes of rat pituitary glands revealed the transformation of different forms of the precursor into different end-products, the anterior lobe producing preferentially ACTH and beta-LPH while the intermediate produces mainly the alpha-MSH and beta-endorphin. The multiple forms of precursors seem to differ in their carbohydrate content although at least two different gene products are still possible. The presence of similar peptides in the hypothalamus makes it highly probable that neuropeptides are biosynthesized with similar process. Thus the model of beta-LPH precursor, proposed as early as in 1967, is now applicable to the biosynthesis of all other neuropeptides. Major advances in this field are expected in the 1980s.

Cushing's syndrome, tryptophan and depression

Fifteen patients with active Cushing's syndrome have been compared with 15 other patients who had been treated successfully for Cushing's syndrome and with 13 patients with other pituitary tumours. Depression was the main psychiatric diagnosis made by the CATEGO programme after Present State Examinations. Patients with active Cushing's syndrome were significantly more depressed (Hamilton Rating Scores), than were the other patients. Compared with the control patients, those with active Cushing's syndrome had slightly lower plasma concentrations of total tryptophan, though the concentrations of freely diffusible tryptophan were not significantly changed.

Isolation of the C-fragment and C'-fragment of lipotropin from pig pituitary and C-fragment from brain

Three novel peptides derived from lipotropin, the C-Fragment (residues 61-91), C'-Fragment (61-87) and N-Fragment (1-38), were isolated from pig pituitary, and the C-Fragment was shown to be present in brain. The experimental procedures developed for their isolation are described. The formation of each of the fragments involves enzymic cleavage of lipotropin at consecutive basic residues, with specificity identical with that involved in the activation of known prohormones. In brain assays C-Fragment exhibits a range of biological activities related to its ability to act as an inhibitory neurotransmitter.