Structure of poly(adenosine diphosphate ribose): identification of 2''-[1''''-ribosyl-2''''-(or 3''''-)(1''''''-ribosyl)]adenosine-5'',5'''',5''''''-tris(phosphate) as a branch linkage.

Poly([14C]adenosine diphosphate ribose) was synthesized from [14C]NAD+ with calf thymus nuclei. The fraction containing poly(adenosine diphosphate ribose) eluted with 0.22--0.40 M phosphate buffer (pH 6.8) from a hydroxylapatite column, was completely hydrolyzed with venom phosphodiesterase, and was separated by DEAE-Sephadex A-25 column chromatography in 7 M urea. A new compound, which constituted 2% of the products from poly(adenosine diphosphate ribose), was found in addition to the expected products--i.e., 5'-AMP, 2'-(1'-ribosyl)adenosine-5',5'-bis(phosphate), and its derivatives. This compound was identified as 2'-[1'-ribosyl 2'-(or 3'-)(1'-ribosyl)]adenosine-5',5',5'-tris(phosphate). The existence of this compound is evidence of a branching structure of poly(adenosine diphosphate ribose), which was previously thought to be a linear molecule. The content of this compound suggests that the frequency of branching is about 1 per 20--30 adenosine diphosphate ribose residues of high molecular weight poly(adenosine diphosphate ribose).