Purified poly(ADP‐ribose) polymerase was inhibited by 1,10‐phenanthroline at pH <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 snowed 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.
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