Diphosphopyridine nucleotide reduction

Diphosphopyridine nucleotide and analogous quaternary pyridinium salts form complexes with bisulphite and with thiols 2-5, xhe orientation of these additions is usually uncertain and may vary with the reaction solvent used " 4, The dithionite addition products formed by quaternary pyridinium salts have attracted interest because of their connection with the dithionite reduction of diphosphopyridine nucleotide (p. 259). Thus, the formation of a 1,4-dihydropyridine (122) by reduction of (120) has been represented 6 as proceeding through a 1,2-addition product (121). Regardless of the correctness or otherwise of structure (121), the relevance of the intermediate for diphosphopyridine nucleotide reduction by dithionite has been questioned, and the yellow intermediate formed in this reaction has been formulated 8 as a charge-transfer complex between the pyridinium nucleus and 820 (see p. 261). 

The reduced form of diphosphopyridine nucleotide (DPNH), which is used in the reduction of di-O-phosphoglyceronic acid to O-phosphoglycerose, could be regenerated with high efficiency from the oxidized form (DPN ) by the reduced form of 6-thioctic acid, thus supplying the necessary re-... 

N4. Nordin, J. H., and Bretthauer, R. K., Colorimetric detection of carriers of galactosemia based on thionicotinamide diphosphopyridine nucleotide (TNDPN) reduction. Federation Proc. 20, 256 (1961). 

The reduction of aromatic nitro compQunds (see p. 98) is also due to the action of an enzyme system in which a dehydrogenase transfers hydrogen to a diphosphopyridine nucleotide-flavoprotein, which in turn reduces the nitro group (Westfall, as well as Bueding and Jolliffe ). 

Two vitamins, nicotinamide and pyridoxine (vitamin B6), are pyridine derivatives. Nicotinamide participates in two coenzymes, coenzyme I (65 R = H) which is known variously as nicotinamide adenine dinucleotide (NAD) or diphosphopyridine nucleotide (DPN), and coenzyme II (65 R = P03H2) also called triphosphopyridine nucleotide (TPN) or nicotinamide adenine dinucleotide phosphate (NADP). These are involved in many oxidation-reduction processes, the quaternized pyridine system acting as a hydrogen acceptor and hydrogen donor. Deficiency of nicotinamide causes pellagra, a disease associated with an inadequately supplemented maize diet. Nicotinic acid (niacin) and its amide are... 

The ring of anthranilic acid, like that of prephenic acid, is derived, in appropriate bacterial extracts, from shikimate 5-phosphate, the amino group originating in the amide nitrogen of glutamine. An oxidation-reduction appears to be involved in this synthesis, since diphosphopyridine nucleotide is a required cofactor. At least one other cofactor, present in yeast extract and so far unidentified, is also required. 

The nicotinamide coenzymes are involved as proton and electron carriers in a wide variety of oxidation and reduction reactions. Before their chemical structures were known, NAD and NADP were known as coenzymes I and II. Later, when the chemical nature of the pyridine ring of nicotinamide was discovered, they were called diphosphopyridine nucleotide (DPN = NAD) and triphospho-pyridine nucleotide (TPN = NADP). The nicotinamide nucleotide coenzymes are sometimes referred to as the pyridine nucleotide coenzymes. 

The irradiation of coenzyme I (diphosphopyridine nucleotide) results in reduction of the pyridine-carbox-amido ring. The product of this reduction is probably a dimer that is itself radiosensitive. 

Aldol dehydrogenases, from diverse species including yeast, horses and humans, catalyze the oxidation of ethanol or the reduction of acetaldehyde, using diphosphopyridine nucleotide (DPN) as a co-factor. Crystalline yeast alcohol dehydrogenase has a molecular weight of 150,000 and contains four Zn2+ ions and binds four DPN molecules per mole. Its structure and chemistry are not yet known in detail. 

Reduction of a-diketones and a-keto esters. Nicotinamide is a component of the coenzymes diphosphopyridine nucleotide (DPN) and triphosphopyridine... 

As indicated in Fig. 1, the initial step in the pathway outlined by Langdon (19,57) was believed to be the condensation of two acetyl CoA units to yield acetoacetyl CoA. Reduction of acetoacetyl CoA then followed, and in this mammalian liver system reduced diphosphopyridine nucleotide w as the hydrogen donor for this reaction. The resulting a-hydroxy-acyl-CoA com-... 

It would be well to point out a few examples which illustrate the overlap of asymmetric reduction studies and molecular biochemistry. Diphosphopyridine nucleotide (DPN) and triphospho-pyridine nucleotide (TPN) are important coenzymes in biochemical oxidation reduction reactions. Certain enzymes function as catalysts for the reversible transfer of hydrogen between these nucleotides and a substrate for which the enzyme is specific. For example, DPN and the enzyme, alcohol dehydrogenase (ADH), form a redox system with ethanol. Using deuterium labeled reducing agent and substrate, Westheimer, Vennesland,... 

Rodkey FL. Oxidation-reduction potentials of the diphosphopyridine nucleotide system. J Biol Chem 1955 213 777-786. 

It is interesting that Udenfriend and Cooper (J.86) had found that an organic alcohol or aldehyde was required in the enzyme system for the oxidized diphosphopyridine to function and that Mitoma ef of. 191) demonstrated that this was required for the reduction of the pyridine nucleotide. In this connection it is to be noted that glucose dehydrogenase stimulates tyrosine formation in the purified enzyme i ystem of Kaufman 190) in the absence of glucose and in the presence of a large excess of TPNH. This enzyme is included in the incubation medium employed by Kaufman. 

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