title: Opioid peptides promote cholera-toxin-catalysed ADP-ribosylation of the inhibitory guanine-nucleotide-binding protein (Gi) in membranes of neuroblastoma x glioma hybrid cells.
abstract: NG108-15 neuroblastoma x glioma hybrid cells express a major 45 kDa substrate for cholera toxin and a 40 kDa substrate(s) for pertussis toxin when ADP-ribosylation is performed in the presence of GTP. In the absence of exogenous GTP, however, cholera toxin was shown to catalyse incorporation of radioactivity into a 40 kDa protein as well as into the 45 kDa polypeptide. In membranes of cells which had been pretreated in vivo with pertussis toxin, the 40 kDa band was no longer a substrate for either pertussis or cholera toxin in vitro, whereas in membranes from cholera-toxin-pretreated cells the 40 kDa band was still a substrate for fresh cholera toxin in vitro and for pertussis toxin. In this cell line, opioid peptides have been shown to inhibit adenylate cyclase exclusively by interacting with Gi (inhibitory G-protein) and with no other pertussis-toxin-sensitive G-protein. Opioid agonists, but not antagonists, promoted the cholera-toxin-catalysed ADP-ribosylation of the 40 kDa polypeptide, hence demonstrating that this cholera-toxin substrate was indeed the alpha-subunit of Gi. These results demonstrate that Gi can be a substrate for either cholera or pertussis toxin under appropriate conditions.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D037361:Adenylate Cyclase Toxin; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006822:Hybrid Cells / Q000378:metabolism; D037342:Pertussis Toxin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D010566:Virulence Factors, Bordetella; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins