Nicotinamide oxygen sensitivity

Anaerobic azo dye reduction can be mediated by enzymes, low molecular weight redox mediators, and chemical reduction by biogenic reductants. These reactions can be located either intracellular or extracellular. Reduction of highly polar azo dyes, which cannot pass through the cell membranes, is located outside the cell. Like azo dyes, nicotinamide adenine dinucleotide phosphate, which is believed to be the main source of electrons, also cannot pass through the cell membranes. Azo reductase enzyme, which is oxygen-sensitive and released extracellularly, is found to be responsible for the reduction of azo dyes. 

In E. coli, ThiH catalyzes the formation of the glycine imine 23 from tyrosine (26). ThiH is an oxygen-sensitive radical 5-adenosyl-L-methionine (SAM) enzyme. Its activity has been reconstituted and the mechanism outlined in Figure 8 has been proposed. It is unclear why E. coli adopts such a complex route to the glycine imine when oxidation of glycine using nicotinamide adenine dinucleotide (NAD) would accomplish the same transformation. 

LDH(PQQ) is a quinoprotein requiring neither oxygen nor nicotinamide cofactors for lactate oxidation. The enzyme has been coupled to a ferrocene-modified carbon electrode (Turner, 1985). The sensor was useful for lactate determination up to 4 mmol/1 but within 5 h the sensitivity dropped to 5%. 

Aune and Pogue344 presented data indicating that at least two distinct mechanisms, (1) stimulation of cellular catabolism of tryptophan and (2) stimulation of cellular catabolism of nicotinamide adenine dinucleotide (NAD) by adenosine diphosphate-ritosyl transferase (ADP-RT), can account for IFN-y-mediated inhibition of tumor cell growth. Both mechanisms appear to be sensitive to oxygen tension and to changes in intracellular glutathione concentrations, and both mechanisms lead to loss of intracellular NAD. 

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