Difference Between NAD+ NADH and NADPH

The key difference between NAD⁺ NADH and NADPH depends on the form in which they exist. NAD⁺ is in the oxidized form while NADH is in the reduced form. On the other hand, NADPH is a reducing agent that has an additional phosphate group than NADH.

Nicotinamide Adenine Dinucleotide (NAD⁺) is a coenzyme present in biological systems. NADH is the reduced form of NAD⁺. Nicotinamide Adenine Dinucleotide Phosphate (NADPH) is also a coenzyme that involves anabolic reactions. It works as a reducing agent in lipid and nucleic acid synthesis. All these NAD⁺, NADH and NADPH are important co-factors in biological reactions. They play a vital role in enzyme-catalyzed metabolic reactions as electron carriers. The purpose of this article is to discuss the difference between NAD⁺ NADH and NADPH.

CONTENTS

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

What is NAD⁺?

Nicotinamide Adenine Dinucleotide (NAD⁺) is a co-enzyme. It has a Vitamin B backbone. Therefore, it is a water-soluble compound. NAD⁺ mainly involves redox reactions. As it is positively charged, it can act as an oxidizing agent. It oxidizes other compounds and converts to its reduced form which is NADH.

NAD⁺  is used in many enzyme-catalyzed reactions, especially in the electron transfer during cellular respiration. Synthesis of NAD⁺ takes place via a denovo pathway using the starting compounds aspartate and tryptophan. Also, synthesis also takes place through modification of niacin which is taken from the diet. Therefore, it is important to have a balanced diet to maintain the levels of NAD⁺ in the body.

What is NADH?

NADH is the reduced form of NAD⁺. It is also a coenzyme. It works as a reducing agent and oxidizes itself while reducing the other compound. Hence, NADH is useful in many catabolic reactions as an electron carrier. Furthermore, NADH acts as a coenzyme in the citric acid cycle.

NADH also acts as a co-factor for many enzymes such as alcohol dehydrogenase, etc. Additionally, NADH has a hepatoprotective activity and plays a role in lowering cholesterol and blood pressure.

Synthesis of NADH is also similar to NAD⁺. Thus, same starting compounds; aspartate and tryptophan involve in the synthesis of NADH. Also, niacin or vitamin B is also involved in the synthesis of NADH.

What is NADPH?

NADPH stands for Nicotinamide Adenine Dinucleotide Phosphate. As the name suggests, in addition to the chemical composition of NADH, there is an additional phosphate group in NADPH. It is a coenzyme which acts as a reducing agent in most reactions mainly in anabolic reactions. Also, it plays an important role in lipid metabolism and nucleic acid metabolism.

Synthesis or generation of NADPH mainly takes place through the pentose phosphate pathway. Also, NADPH is synthesized via the enzyme reaction which uses NADH kinase. In mitochondria, NADH kinase converts NADH into NADPH. In plants, NADPH formation occurs during the light reactions of photosynthesis.

What are the Similarities Between NAD⁺ NADH and NADPH?

• NAD⁺, NADH and NADPH are coenzymes.
• And, they act as electron carriers in metabolic reactions.
• Also, they are derivatives of Vitamin B3 or niacin or nicotinamide.
• Moreover, they participate in redox reactions.
• Besides, they are important to regulate the metabolic reactions in the body.

What is the Difference Between NAD⁺ NADH and NADPH?

NAD⁺ NADH and NADPH are important compounds in living cells which are co-enzymes. NAD⁺ is the oxidized form of NADH while NADH is the reduced form of NAD⁺. NADPH is also a coenzyme which differs from NADH due to the presence of an additional phosphate group. Therefore, this is the key difference between NAD⁺ NADH and NADPH. Moreover, NAD⁺ is an oxidizing agent while NADH and NADPH are reducing agents. Furthermore, NAD⁺ and NADH are participating in catabolic reactions while NADPH is participating in anabolic reactions. Thus, it is another difference between NAD⁺ NADH and NADPH.

A further difference between NAD⁺ NADH and NADPH is that the tryptophan and aspartic acid are the starting compounds of NAD⁺ and NADH synthesis while NADPH synthesis occurs through the pentose phosphate pathway. The below infographic provides more information on the difference between NAD⁺ NADH and NADPH.

Summary – NAD+ vs NADH vs NADPH

NAD⁺ NADH and NADPH are coenzymes which participate in biological reactions. They are derivatives of vitamin B3 or niacin. They participate in redox reactions. In summary of the difference between NAD⁺ NADH and NADPH, the NAD⁺ is in the oxidized form of NADH while NADH is the reduced form of NAD⁺. NADPH, on the other hand, consists of an additional phosphate group than NADH and generates through the pentose phosphate pathway. Furthermore, NAD⁺ and NADH participate in catabolic reactions while NADPH involves in anabolic reactions. Also, NAD⁺ is an oxidizing agent while NADH and NADPH are reducing agents.

Reference:

1. Ying, W. “NAD /NADH and NADP /NADPH in Cellular Functions and Cell Death: Regulation and Biological Consequences.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, Feb. 2008. Available here  

Image Courtesy:

1.”NAD+ Oxidation and Reduction”By JacobShalk – Own work, (CC BY-SA 4.0) via Commons Wikimedia  
2.”NADH phys”By NEUROtiker – Own work, (Public Domain) via Commons Wikimedia  
3.”NADPH”By Tagm2A at French Wikipedia – Own work (Public Domain) via Commons Wikimedia