Pertussis toxin-catalyzed ADP-ribosylation of GTP-binding proteins with digoxigenin-conjugated NAD. Identification of the proteins in plasma membranes and nuclei.

ADP-ribose moiety containing digoxigenin was transferred by pertussis toxin (IAP) to the alpha subunit of Gi (Gi alpha) from digoxigenin-conjugated NAD (DIG-NAD) in a beta gamma subunit-dependent manner. ADP-ribosylation of Gi alpha with DIG-NAD plus IAP was inhibited by native NAD. These results indicate that non-radiolabeled DIG-NAD also serves as the substrate for IAP-catalyzed ADP-ribosylation of G proteins. Using DIG-NAD and fluorescein isothiocyanate-labeled anti-digoxigenin antibody, IAP-sensitive G protein(s) was found to be exist in nuclei as well as plasma membranes of rat liver and HeLa cells. Thus, DIG-NAD is useful to identify pertussis toxin-substrate G proteins.