Increase of mono(ADP-ribose) protein conjugate levels in rat liver induced by nicotinamide administration.

Protein-bound mono(ADP-ribose) residues were quantitated in the livers of nicotinamide-treated and control rats. Nicotinamide administration led to a rise in NAD+ (2.5-fold) and in protein-bound mono (ADP-ribose) residues (1.5-fold). This increase was higher in the NH2OH-sensitive mono(ADP-ribose) protein conjugates than in the NH2OH-resistant subfraction. NADH, NADP and NADPH levels did not change significantly under these conditions. The findings show that nicotinamide induced an increased ADP ribosylation of new acceptor sites, and not merely an elongation of pre-existing (ADP-ribose)n chains. A correlation of the NAD+ concentration and the extent of post-synthetic modification of nuclear proteins by mono(ADP-ribose) residues was not restricted to nicotinamide-induced changes. It was also seen in various tissues with widely differing NAD+ levels.