Solubilized bovine striatal D2 dopamine receptor regulated by sodium ion and guanine nucleotides

Abstract

D2 dopamine receptor was solubilized in a sensitive form for sodium ion and guanine nucleotides with a zwitterionic detergent, 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate (CHAPS), from bovine striatum. The presence of sodium ion in the solubilization mixture markedly increased the yield. The solubilized D2 receptor possessed characteristics of : (a) the site was localized in the striatum but not in the cerebellum; (b) high affinity to nanomolar concentrations of [3H]-spiperone; (c) displacing potencies of various dopamine agonists and antagonists were similar to those of membrane-bound receptors; (d) guanine nucleotides decreased the affinity of soluble receptor for dopamine agonists, but not for antagonists ; (e) negative heterotropic effect of guanine nucleotides was seen only when sodium ion was present in the assay mixture. The solubilized receptor complex was eluted on Sepharose CL-4B column chromatography as a large molecule which had a Stokes radius about 90 Å. Radiation inactivation of membrane-bound D2 dopamine receptor revealed the presence of large (120 0 -1400 K) and small (80 - 100 K) functional units. Therefore, the oligomeric complex between the D2 dopamine receptor and GTP binding protein probably remains intact throughout the solubilization procedure.