tetragastrin

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; E.G., in the conversion of l-phenylalanine to l-tyrosine; the inability to synthesize tetrahydrobiopterin is associated with forms of malignant hyperphenylalaninemia.