The specific binding of vasoactive intestinal peptide (VIP) to bovine thyroid plasma membranes is inhibited by guanine nucleotides. Guanosine 5′-triphosphate (GTP) and the non-hydrolyzable GTP analogs guanosine 5′-β,γ-imidotriphosphate (Gpp(NH)p) and guanosine 5′-O-(3-thiotriphosphate) (GTP-γ-S) inhibited markedly the binding of VIP to its receptors. This inhibition was higher with GTP than with Gpp(NH)p and GTP-γ-S and was due to an increase of the rate of dissociation of peptide bound to membranes. Other nucleotides did not show any effect.

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