What is NADH
NADH refers to the reduced form of NAD. NAD is one of the most abundant types of coenzyme inside the cell, involving in the oxidation-reduction reactions of the cellular respiration. It is mainly used in catabolic reactions. NADH is produced in glycolysis and Krebs cycle. Most dehydrogenases use NAD+ as a coenzyme, donating hydrogen and electrons to produce NADH. NAD+ is the oxidized form of NAD. Two NADHs are produced in glycolysis while six NADHs are produced in Krebs cycle. FADH2 is also produced in Krebs cycle. It also serves as another coenzyme as NADH. Both NADH and FADH2 are used in the electron transport chain. Electron transport chain is shown in figure 1.
Since NADH serves as an electron and hydrogen donor, it donates its electrons to the membrane proteins of the inner mitochondrial membrane. These electrons are used in the production of ATP via oxidative phosphorylation.
What is NADPH
NADPH refers to the reduced form of NADP. NADP is a coenzyme involved in oxidation-reduction reactions of photosynthesis. It is mainly used in anabolic reactions such as nucleic acid and lipid synthesis. NADPH is the most abundant form of NADP inside the cell. It is capable of donating hydrogen and electrons to a chemical reaction. Thereby, NADPH acts as a reducing agent. It structurally differs from NADH by the presence of an additional phosphate group in the 2’ position of ribose, which carries the adenine moiety. The role of NADPH in photosynthesis is shown in figure 2.
NADPH is produced in the light reaction of photosynthesis by the enzyme ferredoxin-NADP+ reductase. Its reduction power is used in the Calvin cycle, assimilating carbon dioxide. In animals, NADP is used in the pentose phosphate pathway.
Difference Between NADH and NADPH
Definition
NADH: NADH is the reduced form of NAD.
NADPH: NADPH is the reduced form of NADP.
Oxidized Form
NADH: NAD+ is the oxidized form of the NADH.
NADPH: NADP+ is the oxidized form of the NADPH.
Involved in
NADH: NADH is involved in cellular respiration.
NADPH: NADPH is involved in photosynthesis.
Produced in
NADH: NADH is produced in glycolysis and Krebs cycle.
NADPH: NADPH is produced in the light reaction of photosynthesis.
Used in
NADH: NADH is used in the electron transport chain to produce ATP by oxidative phosphorylation.
NADPH: NADPH is used in the Calvin cycle to assimilate carbon dioxide.
Free Phosphate Group
NADH: NADH do not contain a free phosphate group.
NADPH: NADPH contains a free phosphate group in the 2’ position of the ribose, which is attached to the adenine moiety.
Type of Reactions
NADH: NADH is involved in anabolic reactions.
NADPH: NADPH is involved in catabolic reactions.
Abundance
NADH: NAD+ is the most abundant form while NADH is less abundant.
NADPH: NADPH is the most abundant form inside the cell.
Conclusion
NADH and NADPH are the reduced forms of the NAD and NADP, respectively. Both NADH and NADPH serve as hydrogen and electron donors for reactions inside the cell. NADH is mainly involved in catabolic reactions whereas NADPH is involved in anabolic reactions. NADH is less abundant in the cell, while NADPH is more abundant in comparison to their oxidized forms. The main difference between NADH and NADPH is the role of each type of reduced coenzyme inside the cell.
