Reinvestigation of the disulfide bridge arrangement in human pro‐opiomelanocortin N‐terminal segment (hNT 1–76)

Abstract
The cystine bridge structure of the amino‐terminal fragment of human proopiomelanocortin has been reinvestigated. Highly purified amino‐terminal fragment 1–76 was rapidly isolated from human pituitaries using only reverse‐phase liquid chromatography (RP‐HPLC). This peptide was then subjected to trypsin and V8‐protease digestion and the products separated by RP‐HPLC> and subjected to amino acid and microsequence analysis. The results show that disulfide bridges link Cys‐2 to Cys‐24 and Cys‐8 to Cys‐20. Amino acid analysis and amino sugar determination confirm (i) the previously proposed sequence and (ii) the suggestion of the presence of two glycosylation sites in this molecule. These are most probably located at Thr‐45 (O‐glycosylation) and at Asn‐65 (N‐glycosylation).