- Xenin
Xenin is a
peptide hormone produced by a subpopulation ofchromogranin A-positive endocrine cells in themucous membrane of theduodenum . The peptide has been found inhumans ,dogs ,pigs ,rats , andrabbits .In humans, xenin circulates in the
blood plasma Feurle GE, Hamscher G, Kusiek R, Meyer HE, Metzger JW.J. Biol. Chem.1992;267:22305-22309] . There is a relationship between peaks of xenin concentration in the plasma and the third phase of theMigrating Motor Complex . For example, infusion of synthetic xenin in fasting volunteers will cause phase III activity. After a meal (the 'postprandial state'), infusion of xenin increases bothcontraction frequency and the percentage ofaboral ly propagated contractions. In higher concentrations xenin stimulates exocrine pancreatic secretion and inhibits thegastrin -stimulated secretion ofacid in dogs. Xenin is also produced inneuroendocrine tumors of the duodenal mucosa."
In vitro ", xenin interacts with theneurotensin receptor 1.tructure and sequence
Xenin is a 25-
amino acid polypeptide. Theamino acid sequence of xenin is identical to theN-terminal end ofcytoplasmic coatomer subunit alpha [http://www.expasy.org/uniprot/P53621 UniProtKB/Swiss-Prot entry P53621 COPA_HUMAN] ] , from which xenin can be cleaved byaspartic protease s. Xenin is structurally related to theamphibian peptidexenopsin and to theneuropeptide neurotensin .Proxenin
Proxenin is the precursor to xenin. It is a 35-amino acid polypeptide. Like xenin, its amino acid sequence exactly matches the N-terminus of
coatomer subunit alpha .References
*Feurle GE, Neurogastroenterol. Mot.2003;13:237-246
*Feurle GE, Anlauf M, Hamscher G, Arnold R, Klöppel G, Weihe B. Gastroenterology 2002;123:1616-1626
*Feurle GE, Ikonomu S,Partoulas G, Stochus B, Hamscher G. Regulatory peptides 2003;111:153-159ee also
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