Xenin--a review.

Xenin, a 25 amino acid peptide, has been identified in human gastric mucosa in the search for a counterpart to the amphibian octapeptide xenopsin. Xenin is structurally related also to the hypothalamic and ileal peptide neurotensin and is, therefore, a member of the xenopsin/neurotensin/xenin peptide family. The biological activities of these peptides are similar: Xenin has been shown to inhibit pentagastrin-stimulated secretion of acid, to induce exocrine pancreatic secretion and to affect small and large intestinal motility. In the gut, xenin interacts with the neurotensin receptor. Radioimmunoassay and chromatography of postprandial plasma in humans indicate the release of xenin into the circulation. The identification of a 35-amino acid precursor peptide of xenin - proxenin, and a review of the Gen-bank revealed that xenin represents the N terminus of a cytosolic coat protein (alpha-COP) from which xenin can be cleaved by aspartic proteinases such as pepsin and cathepsin E. The physiological role of the peptide xenin is not known.