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Solubilization of D2 Dopamine Receptor Coupled to Guanine Nucleotide Regulatory Protein from Bovine Striatum

Abstract: D2 dopamine receptor from bovine striatum was solubilized in a form sensitive to guanine nucleotides, by means of a zwitterionic detergent, 3–[(3‐cholamidopropyl)‐dimethylammonio]‐1 ‐propane sulfonate (CHAPS). The presence of sodium ion markedly increased the solubilization yield. Treatment of the membranes with 10 mM CHAPS and 0.72 M NaCl solubilized 26% of the stereospecific [3H]spiperone binding sites in the original membrane preparations. The solubilized [3H]spiperone binding sites possessed characteristics of the D2 dopamine receptor: (a) localization of the site in the striatum but not in the cerebellum; (b) high affinity to nanomolar concentrations of [3H]spiperone; (c) displacement of [3H]‐spiperone binding by nanomolar concentrations of neuroleptics, but only by micromolar concentrations of do pamine and apomorphine; (d) equal activity of various dopamine agonists and antagonists in the soluble and membrane preparations. Guanine nucleotides decreased the affinity of the solubilized D2 dopamine receptor for dopamine agonists, but not for antagonists. The solubilized receptor complex was eluted in Sepharose CL‐4B column chromajography as a large molecule, with a Stokes radius of ∼90 Å. These results indicate that the complex between the D2 dopamine receptor and GTP binding protein remains intact throughout the solubilization procedure.