J. Biochem, 1988, Vol. 104, No. 5 791-794
© 1988 Japanese Biochemical Society
research-article |
Dopamine D2 Receptors Retain Agonist High-Affinity Form and Guanine Nucleotide Sensitivity after Removal of Sialic Acid1
*Department of Pharmacology, University of Toronto Toronto, Ontario M5S 1A8, Canada
**Department of Psychiatry, University of Toronto Toronto, Ontario M5S 1A8, Canada
2 To whom correspondence should be addressed at the Department of Pharmacology.
The ligand binding subunit of the D2 dopamine receptor (Mr
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.
1 HBN is a Career Scientists of the Ontario Ministry of Health, Health Research Personal Development Program, and KRJ and NHB are recipients of Ontario Mental Health Foundation Research Student-ships. Portions of this work were funded by the Medical Research Council of Canada, the Ontario Mental Health Foundation and the Canadian Friends of Schizophrenics.