Poly(Adenosine Diphosphate Ribose) is Covalently Linked to Nuclear Proteins by Two Types of Bonds

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Abstract
(ADP-ribose)n residues formed by short-term incubation of adult rat liver and Ehrlich carcinoma nuclei with labeled NAD were analyzed by Cs2SO4/guanidinium chloride/urea density gradient centrifugation. Comparison with samples in which the protein was completely digested revealed that most, or probably all, acid-insoluble (ADP-ribose)n chains are covalently bound to nuclear proteins, as it true for the short, acid-soluble (ADP-ribose)n chains. Complete release of (ADP-ribose)n chains is effected by dilute alkali. In contrast, NH2OH liberated only part of the long and the short (ADP-ribose)n residues from the protein conjugates, indicating 2 types of bonds, both alkali-labile, but only 1 susceptible to neutral hydroxylamine. Both types of bonds were eqally distributed among acid-soluble and acid-insoluble (ADP-ribose)n chains. Stability of the (ADP-ribose)n protein conjugates during isolation is only guaranteed at pH values below 7.

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