Two Proteolytic Degradation Products of Calf‐Thymus Poly(ADP‐ribose) Polymerase Are Efficient ADP‐ribose Acceptors

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Abstract
Two polypeptides with molecular masses of 76 and 59 kDa [kilodalton] copurify with poly(ADP-ribose) polymerase from calf thymus, and are efficient acceptors of ADP-ribose as the polymerase itself. Analysis of their CNBr fragments by sodium dodecylsulfate/polyacrylamide gel electrophoresis revealed that the polypeptides were derived from the 112-kDa polymerase. Isolation of poly(ADP-ribose) polymerase in the absence of protease inhibitors resulted in a loss of > 90% of the polymerase activity and an increased proportion of the 76-kDa and 59-kDa polypeptides in the final polymerase preparation. When the polymerase and the 2 polypeptides were separated by gel filtration or polyacrylamide gel electrophoresis in 5% acetic acid, no polymerase activity was found associated with the 2 fragments. Analysis of the CNBr fragments of the 3 polypeptides after incubation of the enzyme preparation with [32P]NAD showed that most of the fragments were radioactive, indicating multiple ADP-ribosylation sites. Several ADP-ribosylated fragments were common to all 3 polypeptides or to 2 of them.