PROOPIOMELANOCORTIN AND ITS PEPTIDE-FRAGMENTS - CLINICAL ASPECTS

Proopiomelanocortin (or POMC), the polypeptide precursor to ACTH, also generates a series of other peptide-fragments during the maturation process which takes place in the normal pituitary and in various POMC-producing pituitary -or non-pituitary-tumors. Thus beta-endorphin-, the lipotropins (beta- and gamma-), the Joining Peptide, the N-terminal fragment all circulate in blood and are valid alternate markers of the overall pituitary corticotropic function. An abnormal maturation of POMC occurs in some non-pituitary tumors releasing aberrant peptide fragments such as beta-MSH5-22 and CLIP (or ACTH18-39). This latter peptide will escape the detection by highly specific ACTH radioimmunoassays and the commercially available two-site immunoradiometric assays.