The glycopeptide domain of the rat vasopressin precursor

The vasopressin precursor is composed of 3 domains, namely vasopressin, MSEL‐neurophysin and a glycopeptide. Processing occurs during axonal transport from hypothalamus to neurohypophysis from which the 3 fragments can be isolated. The glycopeptide fragment of the rat vasopressin precursor has been purified and sequenced. Despite the fact that rat MSEL‐neurophysin is shortened (93 residues instead of 95 for other mammals), rat glycopeptide has 39 residues, as do the other mammalian glycopeptides, suggesting a similar processing. Fifteen substitutions are however observed when compared to ox glycopeptide. The C‐terminal part of MSEL‐neurophysin (residues 77–93) and the glycopeptide are encoded by the same exon and the homologies when compared with their bovine counterparts are 58% and 62% respectively. In contrast, the central part of rat MSEL‐neurophysin (residues 10–76), which is encoded by a separate exon, displays 96% of homology; vasopressin and the N‐terminal part of MSEL‐neurophysin (residues 1–9), encoded by a third exon, are nearly invariant.