Properties of poly(ADP-ribose) synthetase from rat pancreas and poly(ADP-ribosylation) of basic nuclear proteins

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Abstract
The isolated nuclei of rat pancreas contain an enzyme system that will incorporate 3H-labeled NAD into an acid-insoluble product, poly(ADP-ribose). The enzyme has an optimum pH of 7.8 and an optimum temperature of 20-30.degree. C. Optimum Mg2+ concentration is 8 mM and dithiothreitol also stimulates the enzyme at a concentration of 8 mM. Under standard conditions, the Km value for the reaction is 0.25 mM and an inhibition by the substrate is observed at high substrate concentrations. Only 1 basic nuclear protein, histone H1, is modified by the synthetase. An average chain length of 5.0 is found in the nuclei and of 4.5 on histone H1. Radioautographic studies show that poly(ADP-ribose) is closely associated with chromatin.