Structural requirements for gastric inhibitory polypeptide (GIP) receptor binding and stimulation of insulin release.

The effect of bovine GIP 1-42 and several of its fragments in competing with the binding of 125I-GIP to beta-cell plasma membranes from transplantable hamster insulinoma, and in stimulating insulin release from the isolated perfused rat pancreas, was investigated. Our results, in association with the results of previous studies, indicate that the sequence 17-38 is necessary for receptor binding and biological activity of GIP. By contrast, the N-terminal portion of GIP can be removed without seriously impairing the activity of the molecule.