text: The source of ADP-ribose for most enzymes that perform this modification is the redox cofactor NAD. In this transfer reaction, the N-glycosidic bond of NAD that bridges the ADP-ribose molecule and the nicotinamide group is cleaved, followed by nucleophilic attack by the target amino acid side chain. (ADP-ribosyl)transferases can perform two types of modifications: mono(ADP-ribosyl)ation and poly(ADP-ribosyl)ation.