Glutamate substitution for glutamine at position 5 or 6 reduces somatostatin action in the eel intestine.

Isolating a new somatostatin-like peptide from eel gut, the active residues to potentiate somatostatin action in the eel intestine were determined. In the newly-isolated peptide, the 5th or 6th Gln of the eel somatostatin (eSS-25II) was replaced with Glu. Although this peptide also enhanced the short-circuit current (Isc) across the intestine of the seawater eel, higher concentrations (approximately 30 fold) were required to obtain the same effects as eSS-25II. Since the Isc is due to active Cl- transport, this indicates that a structure formed by Gln-Gln residues at position 5 and 6 potentiates the somatostatin action to enhance ion and water transport across the intestine of the eel.