Difference Between NAD and NADP

The key difference between NAD and NADP is that NAD has two phosphate groups, while NADP has three phosphate groups.

ATP is the most important molecule which acts as the universal energy currency of the cell. Apart from that, NAD and NADP molecules are well-known cofactors or coenzymes involved in cellular metabolism, and they serve vital roles in metabolic conversion as signal transducers. NAD and NADP are pyridine nucleotides that contain two nucleotides, adenine base, and nicotinamide. Though NAD and NADP are relatives, they exhibit some differences, as discussed in this article. Structurally, NADP has one additional phosphate group than the NAD.

CONTENTS

1. Overview and Key Difference
2. What is NAD
3. What is NADP
4. Similarities Between NAD and NADP
5. Side by Side Comparison – NAD vs NADP in Tabular Form
6. Summary

What is NAD?

Nicotinamide adenine dinucleotide (NAD) is one of the most important coenzymes found in all living cells. Structurally, it contains two nucleotides joined through their phosphate groups, as shown in Figure 01. One nucleotide has an adenine group, while the other nucleotide contains nicotinamide. There are two known NAD biosynthetic routes. The denovo pathway synthesizes NAD⁺ from aspartate and dihydroxyacetone phosphate or from tryptophan. On the other hand, the salvage pathways utilize degradation products – nicotinic acid and nicotinamide – to produce NAD⁺. The functions of NAD in metabolism are acting as a donor of ADP ribose moieties in ADP ribosylation, as a coenzyme in redox reactions, as a precursor of the second messenger molecule cyclic ADP-ribose, and as a substrate for bacterial DNA ligases.

Moreover, during the redox reactions, NAD converts its reduced form NADP and oxidized form NAD⁺. Furthermore, NAD has a low molecular weight than its relative NADP. Most importantly, NAD lacks the third phosphate group present in NADP.

What is NADP?

NADP is another important cofactor in living cells that predominantly participate in anabolic metabolism. NADP exists in two forms: oxidized form NADP+ and reduced form NADPH. Moreover, NADP synthesis occurs via the phosphorylation of NAD by NADK (NAD Kinase).

In animals, it is a vital molecule of the cellular oxidative defence system and reductive synthesis. NADP molecules play an important role in maintaining a pool of reducing equivalents that is essential to counteract oxidative damage and for other detoxifying reactions. NADPH system can produce free radicals in immune cells that are essential to destroy pathogens in the body. Furthermore, NADP molecules participate in metabolic pathways such as lipid and cholesterol synthesis, and fatty acid elongation in animal cells.

In plants and other photosynthetic organisms, NADPH synthesis takes place in the last step of the electron chain of the light reaction of photosynthesis by ferredoxin-NADP+ reductase enzyme. These NADP then work as the reducing power in the Calvin cycle to assimilate carbon dioxide in plants.

What are the Similarities Between NAD and NADP?

• NAD and NADP are two co-enzymes.
• They participate in cellular metabolism.
• Also, both work as electron carriers.
• And, they can oxidize as well as reduce. Hence, they are involved in redox reaction of the cells.
• Both contain two nucleotides joined together via phosphate groups.

What is the Difference Between NAD and NADP?

NAD and NADP are relative coenzymes. NAD is a coenzyme of living cells that participates mainly in redox reactions of cellular respiration. On the other hand, NADP is another important coenzyme that predominantly participates in redox reactions of anabolic metabolism. So, this is the key difference between NAD and NADP.

Moreover, NADP has an additional phosphate group while this additional phosphate group is absent in the NAD molecule. So, it is also a significant difference between NAD and NADP. Besides, NAD production occurs either in a ‘de novo’ pathway from amino acids or in salvage pathways by recycling nicotinamide back to NAD. On the other hand, NADP biosynthesis requires phosphorylation of NAD catalyzed by NAD kinase. Therefore, we can consider this as another difference between NAD and NADP.

The below infographic summarizes more information on the difference between NAD and NADP.

Summary – NAD vs NADP

NAD and NADP are two most important co-enzymes in living cells. They participate in redox reactions (oxidation and reduction reactions). So, both exist in two forms. The oxidized form of NAD is NAD⁺ while the oxidized form of NADP is NADP⁺. On the other hand, the reduced form of NAD is NADP, while the reduced form of NADP is NADPH. Both have two nucleotides joined together. But, NADP has an additional phosphate group compared to NAD. Thus, this summarizes the difference between NAD and NADP.

Reference:

1. “Nicotinamide Adenine Dinucleotide Phosphate.” Wikipedia, Wikimedia Foundation, 3 June 2019, Available here.
2. “Nicotinamide Adenine Dinucleotide.” Chemistry Explained, Available here.

Image Courtesy:

1. “NAD+ phys” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “NADP+ phys” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia