Molecular characterization of D2 dopamine-like receptors from brain and from the pituitary gland

D2 dopamine-like receptors have been purified from five bovine brain regions (caudate nucleus, putamen, olfactory tubercle, frontal cortex, cerebellum) and the anterior and neurointermediate lobes of the pituitary gland using a combined ligand-affinity and lectin-affinity chromatography procedure. In all the brain regions except cerebellum and in the neurointermediate lobe of the pituitary gland the purified species appeared as a M(r) 95,000 doublet on SDS-PAGE. In the anterior lobe of the pituitary an additional M(r) 142,000-145,000 species was seen. The M(r) 95,000 species had a low affinity for the lectin wheat germ agglutinin (WGA) whereas the M(r) 142,000-145,000 species had a higher affinity for WGA and additionally showed some affinity for concanavalin A. It is concluded that both the M(r) 95,000 and 142,000-145,000 species are D2 dopamine-like receptors and that the differences between the species are mainly at the oligosaccharide level. Some evidence was also obtained for heterogeneity at the protein level which may correspond to the D2(short) and D2(long) isoforms of these receptors.