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Glucagon-like peptide-1 is a gastrointestinal hormone that strongly stimulates insulin release via specific receptors on the pancreatic β-cell. To characterize the side-chain groups required for interaction of glucagon-like peptide-1 with its receptor, we performed binding studies with alanine-substituted glucagon-like peptide-1 analogues on RINm5F insulinoma cells. The binding affinity and biological activity of glucagons-like peptide-1 have been found to be sensitive to alanine exchanges in the N-terminal positions 1, 4, 6 and the C-terminal positions 22 and 23. Alanine substitutions at positions 5, 8, 10–12, 14, 16–21 and 25–30 do not change receptor affinity. These findings could be exploited to design glucagon-like peptide-1 agonists and probably antagonists for further physiological studies. [ABSTRACT FROM AUTHOR]