Endogenous inhibitor of the ADP-ribosylation of (a) G-protein(s) as catalyzed by pertussis toxin is present in rat liver.

The inhibitor activity of the ADP-ribosylation of (a) G-protein(s) as catalyzed by pertussis toxin was found in the membrane extract of rat liver. The inhibitor activity was found in the fractions of DEAE-Sephacel column chromatography at 50-120 mM NaCl. The inhibitor activity is not due to the degradation of NAD nor to the reverse reaction of pertussis toxin (removal of incorporated ADP-ribose). The present result suggests the presence of an endogenous inhibitor of the ADP-ribosylation reaction of (a) G-protein(s).