NAD+/NADH balance

The NAD+/NADH balance of a cell is critical. Cells require sufficient quantities of NAD+ to accept... 

Butanediol is produced during oxygen limited growth by a fermentative pathway known as mixed acid-butanediol pathway (Figure 4) (222). The 2,3-BD pathway and the relative proportions of acetoin and butanediol serve to maintain the intracellular NAD/NADH balance in changing culture conditions. The theoretical... 

A. Santidrian, A. Matsuno-Yagi, M. Ritland, B. Seo, S. LeBoeuf, L. Gay, T. Yagi, and B. Felding-Habermann, Mitochondrial complex I activity and NAD +/NADH balance regulate breast cancer progression, y. Clin. Invest, 123 (2013) 1068-81. 

Glycerol production therefore equilibrates the yeast endocellular oxidation-reduction potential, or NAD+/NADH balance. This relief valve eliminates surplus NADH which appears at the end of amino acid and protein synthesis. 

No living cells can store large amounts of ATP. There is a finite amount of adenine distributed between AMP, ADP and ATP. Thus if the cell has a relatively high concentration of ATP, the concentrations of AMP and/or ADP must be lowered. The balance alters like a "see-saw", as one goes up the other must come down. In addition the total amount of NAD+/NADH and NADP+/NADPH in the cell is constant... 

For each of the reactions in (a) through (f), determine whether the substrate has been oxidized or reduced or is unchanged in oxidation state (see Problem 2). If a redox change has occurred, balance the reaction with the necessary amount of NAD+, NADH, H+, and H20. The objective is to recognize when a redox coenzyme is necessary in a metabolic reaction. 

Klebsiella pneumoniae 1,3-propanediol (1,3-PDO) and 3-hydroxypiDpionic (3-HP) A The simultaneous production of 1,3-PDO and 3-HP can balance the production and consumption of the essential cofiictor, NAD+ (NADH). 38-40... 

But in mammalian species, several mechanisms exist for transferring NADH reducing equivalents, i.e., the malate-aspartate cycle (10) and the a-glycerophosphate-dihydroxy acetone phosphate cycle (16). It seems unlikely that the magnitude of NADH redox transfers due to the interconversions of proline - P5C would alter the N AD+/NADH balance. The oxidation of NADPH by P5C reductase, on the other hand, may play a major role in regulating NADP+/NADPH. Importantly, the of P5C reductase for NADPH is markedly lower than that for NADH (86,117). Although the V .. activities are higher with NADH than with NADPH the conversion of P5C to proline by PC reductase would affect NADP / NADPH more than NAD+/NADH if one considers the respective in vivo concentrations and the respective redox ratios of the two pyridine nucleotides. 

Increased HMP flux also elevates the production of another HMP pathway-associated product, NADPH. The extraNADPH produced via the HMP pathway can then be used to contend with the increased reductive biosynthesis load imposed by increased DNA precursor synthesis. Furthermore, increasing one of the few sources of NADPH in E. coli is an important factor because the dehydrogenases in E. coli are reported to exhibit little cross reactivity between NAD /NADH and NADP/NADPH (Fuhrer and Sauer, 2009). Thus, no transfer of reductant availability from NADH to NADPH via slop in the system can occur and provide a means for making up for shortfalls in NADPH production. However, transhydroge-nase activity, which converts NADH into NADPH, may also help to balance redox metabolism in E. coli. It has been reported that during normal growth, up to 40% of the NADPH used in reductive biosynthesis can be derived from the NADH produced in catabolic reactions (Fuhrer and Sauer, 2009). 

The answer in practice is ATP though you would have been theoretically correct if you had said ADP and AMP. Indirectly, NAD+ or NADH are also compounds which regulate the anabolic/catabolic balance. 

Both competing reductions consume the cofactor nicotinamide adenine dinucleotide (NADH) and thereby interfere with the redox balance of the cell and feedback on glycolysis where NADH is regenerated on the one hand, while on the other hand NAD+ is required to keep the glycolytic pathway running. The nonlinear dynamical model combines the network of glycolysis and the additional pathways of the xenobiotics to predict the asymmetric yield (enantiomeric excess, ee) of L-versus D-carbinol for different environmental conditions (Fig. 3.4). Here, the enantiomeric excess of fluxes vy and i>d is defined as... 

Fig. 8.1 Glucose metabolism in coupled neuron and astrocyte system. ATP is produced via oxidative energy metabolism (glycolysis, TCA cycle and oxidative phosphorylation) in neurons and in astrocytes. Na+ entry during electrical activity initiates increased oxidative energy metabolism within neurons. The activation of neuronal Na+-K+ ATPase in the plasma membrane leads to reduced levels of ATP, which rapidly activates glycolysis. This process requires an elevated glucose level, which is transported via the neuronal glucose transporter (GT). The generated ATP can restore the Na+/K+ balance via Na+-K+ ATPase. The rapid increase of glycolysis results in increased NADH/NAD+ and increased cytoplasmic pyruvate. In astrocytes,...

NADPH balances are often essential for metabolite balancing based estimations of the net fluxes in a metabolic network. However, NADPH consumption and generation are often found in bidirectional reactions that cannot be quantified by metabolite balancing approaches. The mannitol cycle (Fig. 9) is an example of a pathway that can affect the NADPH balance, but has no net conversion of any metabolites, except for cofactors. In the mannitol cycle, NADH and NADP+ are converted into NAD+ and NADPH, respectively, at the expense of ATP [52]. Because mannitol happens to be symmetrical, the activity of the mannitol cycle will cause scrambling of the carbon atoms of fructose 6-phosphate, and the activity of the cycle may therefore be identified using labeling analysis. The mannitol cycle has been reported to be present in several fungi [52]. 

In the balanced chemical equation for glycolysis, two molecules of NAD+ are converted to two molecules of NADH and two protons. The structure of NAD+ (nicotinamide adenine dinucleotide) is given in Fig. 11.1. This is a reduction reaction, and the NAD+, an enzyme cofactor, has accepted the equivalent of H (a hvdride... 

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