| Abstract: | Poly(ADP-ribose) synthetase has been purified approximately 5000-fold from rat liver nuclei. The activity of the purified enzyme is absolutely dependent upon the presence of native or synthetic DNA, and the further addition of histone(s) stimulates the activity 3- to 5-fold. When the ADP-ribosylated material synthesized in the absence or presence of various histones is analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the major product in all cases migrates between histones H1 and H3-H2B with the same RF value of 0.58 relative to the marker dye. No ADP-ribose was found to co-electrophorese with any of thehistones. The addition of histones does not affect the chain number of the poly(ADP-ribose) synthesized but does result in an increase in the average chain length of the polymer. In the presence of histones, the Km for NAD+ decreases from 80 micron to 25 micron and the Vmax doubles. These results indicate that, in the purified poly(ADP-ribose) synthetase system, histones are not ADP-robosylated but act as allosteric activators. |
