sentences:  The modification can be reversed by ADP-ribosylhydrolases, which cleave the N-glycosidic bond between arginine and ribose to release ADP-ribose and unmodified protein; NAD+ is not restored by the reverse reaction.Poly-(ADP-ribose) polymerases (PARPs) are found mostly in eukaryotes and catalyze the transfer of multiple ADP-ribose molecules to target proteins.As with mono-ADP ribosylation, the source of ADP-ribose is NAD+.