Poly(ADP-ribose) polymerase is a catalytic dimer and the automodification reaction is intermolecular.
We have determined the molecular mechanism of the automodification reaction of poly(ADP-ribose) polymerase (PARP) (EC 2.4.2.30). While PARP-mono(ADP-ribose) conjugates were the predominant products of automodification at 200 nM NAD, enzyme-bound branched polymers were preferentially synthesized at 200 microM NAD. Thus, the initiation, elongation, and branching reactions catalyzed by PARP appear to be [NAD]-dependent. Initial rates of automodification increased with second order kinetics as a function of [PARP] at both 200 nM and 200 microM NAD. Therefore, 2 molecules of PARP, i.e. a catalytic dimer, are required for the auto-mono(ADP-ribosyl)ation and the auto-poly(ADP-ribosyl)ation reactions. Initial rates of automodification also increased with second order kinetics at low NAD concentrations. Therefore, the catalytic dimer also requires 2 molecules of NAD. These results are consistent with the conclusion that the automodification reaction of PARP is intermolecular and that the 2 monomeric units of PARP may simultaneously function as catalyst and acceptor molecules in the automodification reaction. Confirmatory evidence for the catalytic role of protein-protein interactions in the automodification reaction was manifested by a marked inhibition of auto-poly(ADP-ribosyl)ation at 40 nM or higher [PARP].
Mendoza-Alvarez
H
H
Department of Microbiology & Immunology, Texas College of Osteopathic Medicine, University of North Texas, Fort Worth 76107-2699.
Alvarez-Gonzalez
R
R
D000818:Animals; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009243:NAD / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D013950:Thymus Gland / Q000201:enzymology*
D046911:Macromolecular Substances; D009243:NAD; D011065:Poly(ADP-ribose) Polymerases