What is the Difference Between NAD+ and NADP+

The main difference between NAD+ and NADP+ is that NAD⁺ is the oxidized state of NAD, which is a coenzyme used in cellular respiration, whereas NADP⁺ is the oxidized state of NADP, which is a coenzyme used in photosynthesis. Furthermore, NAD⁺ does not contain an additional phosphate group on ribose rings while NADP⁺ contains a phosphate group on the 2′ carbon of the ribose ring, which carries the adenine moiety.  

NAD⁺ and NADP⁺ are two oxidized states of coenzymes vital in cellular metabolism. They are responsible for transferring electrons in between biochemical reactions. 

Key Areas Covered 

1. What is NAD+
     – Definition, Structure, Function
2. What is NADP+
     – Definition, Structure, Function
3. What are the Similarities Between NAD+ and NADP+
     – Outline of Common features
4. What is the Difference Between NAD+ and NADP+
     – Comparison of Key Differences

Key Terms 

Cellular Respiration, Coenzyme, NAD⁺, NADP⁺, Photosynthesis, Redox Reactions 

What is NAD+ 

NAD⁺ is the oxidized form of NAD (nicotinamide adenine dinucleotide), which is a coenzyme involved in catabolic reactions as an electron carrier. NADH is the reduced state of NAD. Generally, NAD has two phosphate groups linked by an oxygen molecule. Also, each phosphate group links with a five-carbon, ribose sugar. Furthermore, one ribose sugar links with an adenine nucleotide while the second ribose sugar links with a nicotinamide moiety. Especially, the transition of NAD to NAD⁺ occurs at the nitrogen molecule of the nicotinamide moiety. 

Figure 1: NAD⁺ and NAD

Furthermore, the main function of NAD⁺ is to accept a hydrogen atom or in other words, a proton. Here, accepting a proton represents accepting a pair of electrons. Therefore, NAD⁺ is involved in the redox reactions of cellular respiration including glycolysis, TCA cycle, and electron transport chain. Moreover, both glycolysis and TCA cycle produce NADH whose reduction energy is used in the electron transport chain to generate ATP. In addition, NAD serves as a coenzyme in the reactions in the fatty acid synthesis and sterol synthesis.  

What is NADP+ 

NADP⁺ is the oxidized form of NADP (nicotinamide adenine dinucleotide phosphate), which is a coenzyme involved in anabolic reactions similar to NAD⁺, transferring electrons. NADPH is the reduced state of NADP. Significantly, the structural components of NADP are the same as NAD. However, the main structural difference between NADP and NAD is the presence of an additional phosphate group in the NADP on the 2′ carbon of the ribose ring, which links to the adenine moiety.  

Figure 2: NADP⁺

Moreover, NADP⁺ also accepts a hydrogen atom or in other words, a pair of electrons, during redox reactions. The main types of anabolic reaction which uses NADP⁺ as an oxidizing agent are the Calvin cycle, the dark reaction of photosynthesis. NADPH is synthesized by the light reaction of photosynthesis and its reduction power is used in the dark reaction in order to assimilate carbon dioxide. In addition, NADP is involved in the pentose phosphate pathway in animals as a coenzyme.  

Similarities Between NAD+ and NADP+ 

• NAD⁺ and NADP⁺ are two coenzymes involved in cellular metabolism. 
• Both are in their oxidized state. Therefore, they can obtain electrons released by oxidation reactions, serving as an oxidizing agent.  
• Also, both can exist in their reduced form as well, which release electrons to reduce the product, serving as a reducing agent. 
• Moreover, they are a form of nicotinamide-adenine nucleotides. Also, they contain two ribose rings. 
• Besides, both are abundant inside the cell, transferring electrons between chemical reactions. 
• In addition to the metabolic function, both NADH and NADPH have important physiological functions including gene expression, mitochondrial functions, calcium regulation, antioxidation and the generation of oxidative stress, immune functions, the aging process, and cell death.  

Difference Between NAD+ and NADP+ 

Definition 

NAD⁺ refers to a coenzyme that occurs in many living cells and functions as an electron acceptor while NADP⁺ refers to a coenzyme that functions as a universal electron carrier, accepting electrons and hydrogen atoms to form NADPH or nicotinamide adenine dinucleotide phosphate. Thus, this is the main difference between NAD+ and NADP+.

Structural Difference 

Also, NAD⁺ does not contain any additional phosphate groups on ribose rings, but NADP⁺ contains a phosphate group on the 2′ carbon of the ribose ring, which bears the adenine moiety. 

Reduced State 

Moreover, their reduced state is another difference between NAD+ and NADP+. NADH is the reduced state of NAD⁺ while NADPH is the reduced state of NADP⁺. 

Type of Redox Reactions 

NAD⁺ is involved in catabolic reactions while NADP⁺ is involved in anabolic reactions. 

Function 

Furthermore, NAD⁺ serves as a coenzyme in cellular respiration while NADP⁺ serves as a coenzyme in photosynthesis. Hence, this is another difference between NAD+ and NADP+.

Cellular Fate 

NAD⁺ is reduced to NADH in both glycolysis and TCA cycle, and the reducing power of NADH is used to generate ATP in the electron transport chain. But, NADP⁺ is reduced in the light reaction of photosynthesis and the reducing power of NADPH is used to assimilate carbon dioxide in the dark reaction. So, this is one other difference between NAD⁺ and NADP^+_.

Cellular Ratios 

The NAD⁺: NADH ration is high inside the cell while NADP⁺: NADPH ratio is low inside the cell.

Conclusion 

NAD⁺ is an oxidizing agent used as a coenzyme in catabolic reactions in the cell including cellular respiration. NAD is the reduced form of NAD⁺. In comparison, NADP⁺ is another coenzyme which serves as an oxidizing agent in anabolic reactions including photosynthesis. Its reduced form is NADP. Both NAD⁺ and NADP⁺ are adenine nucleotides involved in the transfer of electrons between redox reactions. However, the main difference between NAD+ and NADP+ is the type of cellular metabolism.

References:

 1. “Nicotinamide Adenine Dinucleotide (NAD).” Kimball’s Biology Pages, 5 Aug. 2003, Available Here
2. “Nadp.” Biology Online, 12 May 2014, Available Here

Image Courtesy:

1. “Figure 07 01 01ab” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia    
2. “NADP+ phys” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia