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Xenin
Xenin is a peptide hormone produced by a subpopulation of chromogranin A-positive endocrine cells in the mucous membrane of the duodenum. The peptide has been found in humans, dogs, pigs, rats, and rabbits.
In humans, xenin circulates in the blood plasma. There is a relationship between peaks of xenin concentration in the plasma and the third phase of the Migrating 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 both frequency and the percentage of aborally propagated contractions. In higher concentrations xenin stimulates exocrine pancreatic secretion and inhibits the gastrin-stimulated secretion of acid in dogs. Xenin is also produced in neuroendocrine tumors of the duodenal mucosa.
''In vitro'', xenin interacts with the neurotensin receptor 1.
==Structure and sequence==
Xenin is a 25-amino acid polypeptide. The amino acid sequence of xenin is identical to the N-terminal end of cytoplasmic coatomer subunit alpha,〔(UniProtKB/Swiss-Prot entry P53621 COPA_HUMAN )〕 from which xenin can be cleaved by aspartic proteases. Xenin is structurally related to the amphibian peptide xenopsin and to the neuropeptide neurotensin.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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