POLY(ADP-RIBOSE) POLYMERASE IN PLANT NUCLEI

We show that poly(ADP-ribose) polymerase is present in maize, pea and wheat nuclei. We have identified the enzyme product as poly(ADP-ribose ) by purification and electrophoresis on a DNA sequencing gel. This re veals a polymer ladder consisting of up to 45 residues. The polymer pr oduct from maize, after digestion with snake venom phosphodiesterase, gave only 5'-AMP and (phosphoribosyl)-AMP; the mean chain length of th e polymer was 5 and 11 residues in two separate experiments. The optim um pH of the plant enzyme is greater than pH 7.0 in pea, wheat and mai ze; the optimum temperature for enzyme activity is approximately 15 de grees C. The K-m for NAD(+) for the enzyme from maize is estimated to be approximately 50 mu M under optimal conditions. Several compounds ( nicotinamide, deoxythymidine, 3-aminobenzamide, 3-methoxybenzamide and 5-bromodeoxyuridine) that specifically inhibit the animal enzyme also inhibit the enzyme from plants. The ratio of the IC50 for 5-bromodeox yuridine to the IC50 for 3-aminobenzamide in maize is similar to that of the animal enzyme indicating that the enzyme involved is poly(ADP-r ibose) polymerase and not mono(ADP-ribosyl) transferase. SDS gel elect rophoresis and gel filtration analysis of a crude extract of maize nuc lei indicate a molecular mass for poly(ADP-ribose) polymerase of appro ximately 114 kDa.