tetragastrin

tet·ra·gast·rin

(tet'ră-gas'trin), 1. A tetrapeptide (Trp-Met-Asp-Phe-NH2) used to test the secretion of digestive juice. 2. A pterin derivative that is a required cofactor for a number of enzymes; for example, in the conversion of l-phenylalanine to l-tyrosine; the inability to synthesize tetrahydrobiopterin is associated with forms of malignant hyperphenylalaninemia.