title: A-protein catalyzes the ADP-ribosylation of G-protein from cow rod outer segments.
abstract: A 20-kilodalton adenosine nucleotide-binding protein (A-protein) extracted from rod outer segments is shown to catalyze the cholera toxin-mediated ADP-ribosylation of GTP-binding protein (G-protein) from the outer segment. Radiolabel from [adenylate-32P] NAD+ was associated specifically with both the alpha-subunit of G-protein and with A-protein in the presence of activated cholera toxin. In the absence of added A-protein, G-protein appears to undergo ADP-ribosylation at a slower rate. In the absence of G-protein, A-protein was found to be labeled following incubation with [adenylate-32P]NAD+ and cholera toxin. In the presence of G-protein, a light-dependent component of A-protein labeling was observed. A-protein is a labile component of rod outer segments and has an affinity for ADP. The findings suggest that A-protein may act as an ADP-ribosyltransferase in the cholera toxin-mediated ADP-ribosylation of G-protein.
mesh_terms: D036002:ADP Ribose Transferases; D020727:ADP-Ribosylation Factors; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D002772:Cholera Toxin / Q000494:pharmacology; D005136:Eye Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010430:Pentosyltransferases / Q000378:metabolism*; D010786:Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D005136:Eye Proteins; D046911:Macromolecular Substances; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D036002:ADP Ribose Transferases; D010430:Pentosyltransferases; D019204:GTP-Binding Proteins; D020727:ADP-Ribosylation Factors