NADH—See Nicotinamide adenine dinucleotide

NADH (reduced nicotinamide adenine dinucleotide) is utilized in biological reductions to deliver hydride to an aldehyde or ketone carbonyl group (see Box 7.6). A proton from water is used to complete the process, and the product is thus an alcohol. The reaction is catalysed by an enzyme called a dehydrogenase. The reverse reaction may also be catalysed by the enzyme, namely the oxidation of an alcohol to an aldehyde or ketone. It is this reverse reaction that provides the dehydrogenase nomenclature. 

Glucose [50-99-7] urea [57-13-6] (qv), and cholesterol [57-88-5] (see Steroids) are the substrates most frequentiy measured, although there are many more substrates or metaboUtes that are determined in clinical laboratories using enzymes. Co-enzymes such as adenosine triphosphate [56-65-5] (ATP) and nicotinamide adenine dinucleotide [53-84-9] in its oxidized (NAD" ) or reduced (NADH) [58-68-4] form can be considered substrates. Enzymatic analysis is covered in detail elsewhere (9). 

Figure 18.2 Summary of respiratory energy flows. Foods ate converted into the reduced form of nicotinamide adenine dinucleotide (NADH), a strong reductant, which is the most reducing of the respiratory electron carriers (donors). Respiration can he based on a variety of terminal oxidants, such as O2, nitrate, or fumarate. Of those, O2 is the strongest, so that aerobic respiration extracts the largest amount of free energy from a given amount of food. In aerobic respiration, NADH is not oxidized directly by O2 rather, the reaction proceeds through intermediate electron carriers, such as the quinone/quinol couple and cytochrome c. The most efficient respiratory pathway is based on oxidation of ferrocytochrome c (Fe ) with O2 catalyzed by cytochrome c oxidase (CcO). Of the 550 mV difference between the standard potentials of c)Tochrome c and O2, CcO converts 450 mV into proton-motive force (see the text for further details).

A coenzyme is an organic compound that activates the primary enzyme to a catalytically active form. A coenzyme may act as a cofactor (see footnote 2), but the converse is not necessarily true. For example, the coenzyme nicotinamide adenine dinucleotide, in either its oxidized or reduced forms (NAD+ or NADH), often participates as a cofactor in enzyme reactions. 

NADH. See also Nicotinamide adenine dinucleotide (NADH) biosensors for, 3 797 requirement as cofactor, 3 672-673 Nadic group, in creating polyimide thermosetting resins, 20 275... 

Nicotinamide adenine dinucleotide (NADH), 24 348. See also NADH Nicotinamide adenine dinucleotide... 

See also NAD+, NADH NADP+, NADPH daily requirements 756, 769 Nicotinamide adenine dinucleotide. See NAD+, NADH... 

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

When the dehydrogenases are used in analysis the method relies on measuring the change in the redox state of the cofactor, i.e. the change in the concentration of NAD or NADH. NADH is inherently more easily detected photometrically and electrochemically (see below) than its oxidized counterpart, NAD+ 13). When catalyzed by a dehydrogenase, the redox reaction of the nicotinamide adenine dinucleotides (NAD(P)+/NAD(P)H) is reversible, see Figure 1. A reaction catalyzed by a dehydrogenase can be schematically written as follows ... 

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