title: Dopamine D2 receptors retain agonist high-affinity form and guanine nucleotide sensitivity after removal of sialic acid.
abstract: The ligand binding subunit of the D2 dopamine receptor (Mr approximately equal to 94,000) can be visualized by autoradiography following photoaffinity labeling with [125I]N-azidophenethylspiperone and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Following removal of sialic acids with the exoglycosidase, neuraminidase, [125I]N-azidophenethylspiperone photoincorporated into a protein of Mr = 54,000 with the appropriate pharmacological profile for D2 receptors. The desialylated D2 receptor bound dopaminergic agonists with high affinity and was capable of coupling to a functional G-protein as indexed by: 1) pertussis-toxin mediated [32P]ADP ribosylation of proteins of Mr = 42,000 and 39,000, and 2) the conversion of the agonist high affinity form of D2 receptors to one displaying low affinity for agonists in the presence of guanine nucleotides. These data suggest that sialic acid residues do not contribute significantly to the ligand binding characteristics of D2 receptors despite the large change produced in the estimated molecular mass of the binding subunit.
authors.affiliation: Department of Pharmacology, University of Toronto, Ontario, Canada.
authors.forename: K R
authors.initials: KR
authors.lastname: Jarvie
authors.forename: H B
authors.initials: HB
authors.lastname: Niznik
authors.forename: N H
authors.initials: NH
authors.lastname: Bzowej
authors.forename: P
authors.initials: P
authors.lastname: Seeman
mesh_terms: D000345:Affinity Labels; D000818:Animals; D001386:Azides; D003342:Corpus Striatum / Q000378:metabolism; D004285:Dogs; D015259:Dopamine Agents / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008970:Molecular Weight; D009439:Neuraminidase / Q000378:metabolism; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism*; D017448:Receptors, Dopamine D2; D012794:Sialic Acids / Q000502:physiology*; D013134:Spiperone / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D000345:Affinity Labels; D001386:Azides; D015259:Dopamine Agents; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D012794:Sialic Acids; D013134:Spiperone; C044567:N-(4-azido-3-iodophenethyl)spiperone; D009439:Neuraminidase; D019204:GTP-Binding Proteins