Characterization of glucagon-like peptide-I(7-36)amide receptors of rat lung membranes by covalent cross-linking.

125I-labelled GLP-I(7-36)amide was cross-liked to a specific binding protein in rat lung membranes using disuccinimidyl suberate. A single radio-labelled band at Mr 66,000 was identified by SDS-PAGE after solubilization of the ligand-binding protein complex which is consistent with the presence of a single class of binding sites on rat lung membranes. The band was undetectable when 1 mumol/l GLP-I(7-36)amide was included in the binding assay. No change in the mobility of the band was observed under reducing conditions suggesting that the binding protein in the receptor is not part of a larger disulphide-linked protein. The intensity of the radiolabelled protein band was reduced when the incubation with 125I-labelled GLP-I(7-36)amide was carried out in the presence of guanine nucleotides suggesting that the GLP-I(7-36)amide receptor is coupled to the adenylate cyclase system.