Effect of polyamines on two types of reaction of purified poly(ADP-ribose) polymerase.

The effects of polyamines on reactions catalyzed by bovine thymus poly(ADP-ribose) polymerase were examined under various conditions, and the following results were obtained. (1) Spermine and spermidine, and putrescine to a lesser degree can stimulate the synthesis of poly(ADP-ribose) covalently bound to the enzyme without Mg2+ and histones. (2) A part of the above stimulation can be explained by the Mg2+-sparing effect of polyamines. (3) The other part of the stimulation is shown to be through protection of the enzyme against the formation of an abortive complex of the enzyme and denatured DNA, which contaminates some native DNA preparations used for enzyme activation. Similar protection was shown earlier in this laboratory with histones. (4) Putrescine seems to lack this enzyme-protecting activity. (5) The polyamine effect observed in the Mg2+-dependent reaction is variable depending on the DNA preparations used. (6) Chemical analysis shows that the average chain lengths of the products synthesized with Mg2+ and spermine are similar, and the products are covalently bound to the enzyme, indicating that the reaction supported by polyamines is essentially the same as that by Mg2+. (7) Under the histone H1-dependent reaction conditions where ADP-ribosylation of histone H1 is predominant, both Mg2+ and polyamines are inhibitory on the reaction and both cations decrease the number of product molecules without affecting the size of the product. These data suggest that polyamines can at least partially replace Mg2+ in terms of effect on the ADP-ribosylation reaction. The other effect of polyamines is the protection of the enzyme from abortive binding to denatured DNA, as has also been shown to occur with histones.