Bombesin and structurally related peptides including gastrin releasing peptide (GRP) are potent mitogens for Swiss 3T3 cells. Here we attempted to solubilize bombesin receptors under conditions in which the ligand (125I-labelled GRP) was prebound to the receptor prior to detergent extraction. We found that 125I-GRP-receptor complexes were solubilized from Swiss 3T3 cell membranes by using the detergents taurodeoxycholate or deoxycholate. These detergents promoted ligand-receptor solubilization in a dose-dependent manner. In contrast, a variety of other detergents including Triton X-100, octylglycoside, CHAPS, digitonin, cholic acid and n-dodecyl-β-D-maltoside, were much less effective. Addition of guanosine 5'-[γ-thio]triphosphate (GTPγS) to ligand-receptor complexes isolated by gel nitration enhanced the rate of ligand dissociation in a concentration-dependent and nucleotide-specific manner. Our results demonstrate for the first time the successful solubilization of 125 I-GRP-receptor complexes from Swiss 3T3 cell membranes and provide evidence for the physical association between the ligand-receptor complex and a guanine nucleotide binding protein(s).
