Pyridine nucleotide transhydrogenase from Chromatium.

The isolation and purification of a soluble transhydrogenase from Chromatium is described. The enzyme promotes the oxidation of reduced triphosphopyridine nucleotide by diphosphopyridine nucleotide. However, it will also use several analogues of DPN and TPN which include deamino-DPN, deamino-TPN, thionicotinamide DPN, and deamino-DPNH. Nicotinamide mononucleotide was also reduced. The enzyme does not use the 3-acetylpyridine analogues as substrates. TPN and adenosine P’-phosphate were shown to be competitive inhibitors of the enzyme with TPNH or DPNH as the hydrogen donor. The enzyme is inhibited by mercaptide-forming reagents. The enzyme is compared with previously described transhydrogenases and a possible role in metabolism is discussed.