Diphosphopyridine nucleotide, formation

Ascorbic acid depleted from adrenal cortex or ovary on progesterone formation Niacin diphosphopyridine nucleotide (DPN) involved in progesterone synthesis... 

Carhodiimidazole-Catalyzed Chemical Synthesis of Arylazido Adenine Nucleotide Analogs. The utilization of carbodiimidazole to facilitate the formation of activated carboxylic acids was elegantly applied by Gottikh and his group to the synthesis of a wide spectrum of aminoacyl nucleosides, nucleotides, nucleoside di- and triphosphates, and tRNA derivatives. The formation of an imidazolide intermediate has been used in our work in the synthetic schemes leading to the esterification of adenosine and diphosphopyridine nucleotides. 

With our sensitive spectrophotometric methods (11,12,17) we have shown how the reaction velocity constants for peroxidase action can be measured directly from the kinetics of formation and disappearance of the enzyme-substrate complex. This is perhaps the most elegant and incisive method of assay and can now be successfully applied not only to hemo-proteins but also to diphosphopyridine nucleotide enzymes. The detaUs of the methods lie outside the scope of this review and are available in detail elsewhere (3,6). 

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). 

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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