Solubilization from rat pancreatic plasma membranes of a cholecystokinin (CCK) agonist‐receptor complex interacting with guanine nucleotide regulatory proteins coexisting in the same macromolecular system

Using the non-denaturing detergent 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propane sulfonate (Chaps), cholecystokinin (CCK) receptors were solubilized from rat pancreatic membranes as a reversible complex with the CCK 31–39 nonapeptide 125I-labelled by the Bolton and Hunter reagent. Bound ligand dissociation from this soluble complex was similar to that from the membranous receptors of origin and the marked increase in the rate of dissociation induced by GTP was preserved in the soluble state, indicating that the solubilized CCK receptors remained functionally coupled with the guanine nucleotide regulatory site modulating the affinity for CCK. In fact, two guanine nucleotide regulatory proteins, Ns and Ni, coexisted in the soluble complex as established by identifying the 42-kDa subunit of Ns and the 40-kDa subunit of Ni, after ADP-ribosylation by cholera toxin and Bordetella pertussis toxin, respectively.