Poly(ADP-ribose) polymerase is a zinc metalloenzyme.

Purified poly(ADP-ribose) polymerase was inhibited by 1,10-phenanthroline at pH less than 8. This inhibition and the inhibition by other chelating agents suggested that this enzyme was a metalloprotein. Atomic absorption spectroscopy showed the presence of one atom of zinc per protein molecule. Dialysis of the enzyme against buffers containing 1,10-phenanthroline resulted in the loss of activity and the removal of zinc from the enzyme. Initial rate kinetics showed that 1,10-phenanthroline was non-competitive with NAD+ and competitive with DNA. The binding of DNA to the enzyme was unaffected by the inhibitor. These results suggest that a metal-containing site is involved as part of the interaction of DNA and poly(ADP-ribose) polymerase.