NAD, NADH, NADP, NADPH

Examples of coenzymes vitamin-derived nucleotides for example adenosine phosphates ATP, ADP, AMP nicotinamide derivatives NAD+, NADH, NADP+, NADPH flavin derivatives FAD, FADH2 coenzyme A (abbreviated to CoA, CoASH or CoA-SH). 

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

The following coenzymes contain the AMP moiety NAD+, NADH, NADP+, NADPH, FAD, FADH2, and CoASH. 

Source Ref. i Glutamate a-Keto- glutarate NH 4+ NAD NADH NADP NADPH ... 

NAD, NADH, NADP, NADPH. Abbreviations for nicotinamide adenine dinucleotide [phosphate] in the oxidized and reduced forms, see nicotinamide coenzymes. 

Many of the enzymes involved in metabolic pathways require coenzymes to act as carriers of electrons, atoms or groups of atoms. The coenzymes act alternately as acceptors and donors and exist in alternative states, e.g. NAD /NADH, NADP /NADPH, pyridoxal/pyridoxamine, CoA/acetyl-CoA. Since coenzymes are in effect cosubstrates that react with the substrate in stoichiometric proportions, the question of which of the two forms predominates may be decisive in determining the direction of reactions occurring at or near equilibrium. Specific portions of some metabolic pathways may be controlled in this way, e.g. the conversion of pyruvate to lactate in muscles during physical exertion. 

Table 1 NAD (NAD+ + NADH) and Total Nicotinamide (Free Nicotinamide + NAD + NADH + NADP+ + NADPH) Levels in Various Tissues of Rats... 

In cytoplasm, the NADP+ NADPH ratio corresponds to 1 X 10 while the NAD+ NADH ratio is approximately 1 X 10 . Consequently, the (NAD" NADH) (NADP NADPH) ratio is approximately 1 X 10 . The NAD" NADH ratio in mitochondria—corresponding to the NADP" " NADPH ratio—appears to be about 100 times smaller than that in the rat liver cytoplasm (Veech et al., 1969). In white adipose tissue, most of the NADPH is recovered in supernatant -I- microsomes (MacLean et al., 1967), while NADH is approximately twice as concentrated in mitochondria as in supernatant. The (NAD+ NADH) (NADP NADPH) ratio in cytoplasm corresponds approximately to 1. 

Niacin NAD, NADH, NADP, NADPH Dehydrogenases reductases Many pathways, particularly /1-oxidation and fatly-acid synthesis and elongation... 

Nicotinamide nucleotide transhydrogenase, which catalyzes the reaction NADPH + NAD+ NADH + NADP+, spans the membrane, but its catalytic site faces the M side. 

Many different systems have heen suggested for the regeneration of (mostly) one of the coenzymes NAD, NADH, NADP or NADPH. Only a few publications which appeared after the review articles of the Whitesides group (87-89) shall be mentioned (90,91). For the photochemical and electrochemical regeneration of nicotinamide cofactors see (92,93). 

In crude cell extracts of C. thermoaceticum the specific activity of AMAPORs for NADP reduction with reduced MV is extraordinarily high and more than twice of that for NAD. NADH and NADPH dehydrogenation for the regeneration of NAD and NADP is achieved with the same enzyme activities and anthraquinone-2,6-disulphonate (Reaction [31a]). The activities are about the same as for carbamoylmethylviologen (CAV) (Table 24). 

Chromatographic analysis of NAD+, NADH, NADP, and NADPH is not practical because these compounds are not stable. In biological materials they are mea-... 

Klaidman et al. (38) reported a fluorometric ultrasensitive HPLC method for NAD+, NADH, NADP, and NADPH. The oxidized nucleotides were transformed to stable fluorescent products with cyanide in a basic solution. A chromatogram of a reference mixture of NAD and the related compounds is shown in Figure 13. In our laboratory, standard NAD, NADPH, NADP, and NADPH have been reported using HPLC as shown in Figure 14. 

Nicotinamide is an essential part of two important coenzymes nicotinamide adenine dinucleotide (NAD ) and nicotinamide adenine dinucleotide phosphate (NADP ) (Figure 18.19). The reduced forms of these coenzymes are NADH and NADPH. The nieotinamide eoenzymes (also known as pyridine nucleotides) are electron carriers. They play vital roles in a variety of enzyme-catalyzed oxidation-reduction reactions. (NAD is an electron acceptor in oxidative (catabolic) pathways and NADPH is an electron donor in reductive (biosynthetic) pathways.) These reactions involve direct transfer of hydride anion either to NAD(P) or from NAD(P)H. The enzymes that facilitate such... 

The coenzyme for the oxidation-reduction reactions of fatty acid synthesis is NADP /NADPH, whereas degradation involves the NAD /NADH couple. 

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... 

NAD+ and NADP+ are coenzymes of dehydrogenases. NADH and NADPH are intermediate carriers of both hydrogen and electrons. Most NAD-dependent enzymes are located in the mitochondria and deliver H2 to the respiratory chain whereas NADP-dependent enzymes take part in cytosolic syntheses (reductive biosyntheses). 

Mudd, Mudd et Menzel, and Nasr et have reported that ozonization of aqueous solutions of NADH or NADPH results in their oxidation. However, there is a difference in their findings as to whether the resulting product is a biologically active oxidized pyridine nudeotide (NAD or NADP), as suggested by Menzel, or is molecularly disrupted to the extent that it is unable to participate in enzymatic processes. Inasmuch as more drastic effects are likely to be observed in vitroy it is more likely that oxidation of intracellular reduced pyridine nucleotides proceeds mainly to NAD or NADP after ozone inhalation but further resolution of this question would be of value. 

Tab. 13.6 Overview of retentions of various membranes for NAD, NADP, NADH and NADPH in different solutions.

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