Purification and properties of dinitrogenase reductase ADP-ribosyltransferase from the photosynthetic bacterium Rhodospirillum rubrum.

The enzyme that catalyzes the ADP-ribosylation and concomitant inactivation of dinitrogenase reductase in Rhodospirillum rubrum has been purified greater than 19,000-fold to near homogeneity. We propose dinitrogenase reductase ADP-ribosyltransferase (DRAT) as the working name for the enzyme. DRAT activity is stabilized by NaCl and ADP. The enzyme is a monomer with a molecular mass of 30 kDa and is a different polypeptide than dinitrogenase reductase activating glycohydrolase. NAD (Km = 2 mM), etheno-NAD, nicotinamide hypoxanthine dinucleotide, and nicotinamide guanine dinucleotide will serve as donor molecules in DRAT-catalyzed ADP-ribosylation reaction, and dinitrogenase reductases from R. rubrum, Azotobacter vinelandii, Klebsiella pneumoniae, and Clostridium pasteurianium will serve as acceptors. No other proteins or small molecules, including water, have been found to be effective as acceptors. Nicotinamide is released stoichiometrically with formation of the ADP-ribosylated product. DRAT is inhibited by NaCl and has maximal activity at a pH of 7.0.