Interaction of GTP-binding regulatory proteins with chemosensory receptors.
GTP-binding regulatory proteins (G-proteins) were identified in chemosensory membranes from the channel catfish, Ictalurus punctatus. The common G-protein beta-subunit was identified by immunoblotting in both isolated olfactory cilia and purified taste plasma membranes. A cholera toxin substrate (Mr 45,000), corresponding to the G-protein that stimulates adenylate cyclase, was identified in both membranes. Both membranes also contained a single pertussis toxin substrate. In taste membranes, this component co-migrated with the alpha-subunit of the G-protein that inhibits adenylate cyclase. In olfactory cilia, the Mr 40,000 pertussis toxin substrate cross-reacted with antiserum to the common amino acid sequence of G-protein alpha-subunits, but did not cross-react with antiserum to the alpha-subunit of the G-protein from brain of unknown function. The interaction of G-proteins with chemosensory receptors was determined by monitoring receptor binding affinity in the presence of exogenous guanine nucleotides. L-Alanine and L-arginine bind with similar affinity to separate receptors in both olfactory and gustatory membranes from the catfish. GTP and a nonhydrolyzable analogue decreased the affinity of olfactory L-alanine and L-arginine receptors by about 1 order of magnitude. In contrast, the binding affinities of the corresponding taste receptors were unaffected. These results suggest that olfactory receptors are functionally coupled to G-proteins in a manner similar to some hormone and neurotransmitter receptors.
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000409:Alanine / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000378:metabolism; D002397:Catfishes; D002628:Chemoreceptor Cells / Q000378:metabolism*; D002772:Cholera Toxin / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism; D007163:Immunosorbent Techniques; D008565:Membrane Proteins / Q000378:metabolism; D008970:Molecular Weight; D011984:Sensory Receptor Cells / Q000378:metabolism*
D006150:Guanine Nucleotides; D008565:Membrane Proteins; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D001120:Arginine; D019204:GTP-Binding Proteins; D000409:Alanine