NADH biological functions

Despite the apparent simplicity of their structures, the chemistry of the nicotinamide ring in NAD+ and NADP+ is surprisingly complex.128 129 NAD+ is extremely unstable in basic solutions, whereas NADH is just as unstable in slightly acidic media. These properties, together with the ability of NAD+ to undergo condensation reactions with other compounds, have sometimes caused serious errors in interpretation of experiments and may be of significance to biological function. 

The use of activated carriers illustrates two key aspects of metabolism. First, NADH, NADPH, and FADH react slowly with Oj in the absence of a catalyst. Likewise, ATP and acetyl CoA are hydrolyzed slowly (in times of many hours or even days) in the absence of a catalyst. These molecules are kinetically quite stable in the face of a large thermodynamic driving force for reaction with O2 (in regard to the electron carriers) and H O (for ATP and acetyl CoA). The kinetic stability of these molecules in the absence of specijic catalysts is essential for their biological function because it enables, enzymes to control the flow of free energy and reducing power. 

NADH is present in every living cell, where it catalyzes more than 1000 biochemical reactions. The most important biological functions of NADH are the following ... 

NADH has been shown to inhibit the growth of murine fibrosarcoma and human laryngeal carcinoma cells in vitro.Based on these findings and the various biological functions, the stabilized oral form of ENADA has been used as treatment for certain... 

Ubiquinones function within the mitochondria of cells to mediate the respiration process in which electrons are transported from the biological reducing agent NADH to molecular oxygen. Through a complex series of steps, the ultimate result is a cycle whereby NADH is oxidized to NAD+, O2 is reduced to water, and energy is produced. Ubiquinone acts only as an intermediary and is itself unchanged. 

Sambongi Y, Nitta H, Ichihashi K, Futai M, Ueda I (2002) A novel water-soluble Hantzsch 1,4-dihydropyridine compound that functions in biological processes through NADH regeneration. J Org Chem 67 3499-3501... 

The nicotinamide coenzymes are biological carriers of reducing equivalents (electrons). The most common function of NAD+ is to accept two electrons and a proton (H equivalent) from a substrate undergoing metabolic oxida-tion to produce NADH, the reduced form of the coenzyme. This then diffuses or is transported to the terminal-electron transfer sites of the cell and reoxidized by terminal-electron acceptors, 02 in aerobic organisms, with the concomitant formation of ATP (chapter 14). Equations (8), (9), and (10) are typical reactions in which NAD+ acts as such an acceptor. 

Solomonson, L.P., Barber, M.J., Robbins, A.P. Oaks, A. (1986). Functional domains of assimilatory NADH nitrate reductase from Chlorella. Journal of Biological Chemistry 261, 11290-4. 

A number of functional groups, such as nitro, diazo, carbonyls, disulfides, sulfoxides, and alkenes, are susceptible to reduction. In many cases it is difficult to determine whether these reactions proceed nonenzymatically by the action of biological reducing agents such as NADPFI, NADH, and FAD or through the mediation of functional enzyme systems. As noted above, the molybdenum hydroxylases can carry out, in vitro, a number of reduction reactions, including nitro, azo, A-oxidc, and sulfoxide reduction. Although the in vivo consequences of this are not yet clear, much of the distribution of reductases described below may be, in whole or in part, the distribution of molybdenum hydroxylases. 

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