Enzymatic studies with analogues of diphosphopyridine nucleotide.

It has been previously shown (l-3) that the nicotinamide moiety of diphosphopyridine nucleotide can be replaced by other pyridine bases without the loss of the coenzyme function. The observation that both the 3-acetylpyridine and pyridine-3aldehyde analogues of diphosphopyridine nucleotide function as coensymes with various dehydrogenases (3) indicated that the amide group on DPN was not essential for DPN activity or more specifically, the amino portion of the amide group of DPN was not essential for the coenzyme function. Other coenzyme analogues having groups in position 3 of the pyridine moiety not containing a carbonyl function (such as the /3-picoline, 3-pyridylmethylcarbinol and 3-pyridylcarbinol analogues) were shown not to be enzymatically reduced (3). Recently a new series of DPN analogues was prepared and its chemical properties investigated (4). The chemical reactiviby of the majority of these dinucleotides in addition reactions suggested the possibility that they could serve as coenzymes in dehydrogenase systems. A preliminary study involving several of these coenzyme analogues in dehydrogenase systems was recently presented (5). The present paper constitutes an extension of these studies to include observations obtained with these DPN analogues in several other enzyme-catalyzed reactions. Data will be presented to demonstrate the nonessentiality of the entire amide group of DPN in dehydrogenase reactions.