Reducing equivalent

In biochemistry, the term reducing equivalent refers to any of a number of chemical species which transfer the equivalent of one electron in redox reactions.[1] A redox reaction (oxidation-reduction reaction) results in a change of oxidation state of atoms or ions due to actual or formal transfer of electrons. A chemical species is reduced when it gains electrons and is oxidized when it loses electrons.[2] A reducing equivalent serves as the electron donor in a redox reaction and becomes oxidized (loses electrons) when it donates an electron to an electron acceptor.[3] A reducing equivalent can donate an electron in multiple ways: as a lone electron, as a hydrogen atom, as a hydride ion, or by bond formation with an oxygen atom.[4]

Reducing equivalents in the mitochondrial respiratory chain

Oxidative phosphorylation is the process driving ATP synthesis by means of the energy of O2 [9] released through the oxidation of reducing equivalents. It occurs in the mitochondrial electron transport chain,[10][4] which is located at the inner mitochondrial membrane and consists of transmembrane protein complexes that catalyze redox reactions.[11] NADH and FADH2 are reducing equivalents that donate electrons at complexes I and II, respectively. These electrons are then transferred in multiple redox reactions and are carried to the complexes III and IV.[3][12] The oxidation of reducing equivalents in the electron transport chain releases protons into the intermembrane space of the mitochondria and maintains the proton electrochemical gradient.[3][4] As protons move down the electrochemical gradient through the transmembrane protein ATP synthase, ATP is generated from ADP and an inorganic phosphate group.[3][4] In order to maintain the proton gradient and generate ATP, reducing equivalents are supplied to the electron transport chain from multiple processes such as the TCA cycle.[13]

Reducing equivalents NADH and FADH2 donating electrons at the electron transport chain for oxidative phosphorylation.

See also

References
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  9. Schmidt-Rohr, K. (2020). "Oxygen Is the High-Energy Molecule Powering Complex Multicellular Life: Fundamental Corrections to Traditional Bioenergetics” ACS Omega 5: 2221-2233. http://dx.doi.org/10.1021/acsomega.9b03352
  10. Kehrer JP, Lund LG (July 1994). "Cellular reducing equivalents and oxidative stress". Free Radical Biology & Medicine. 17 (1): 65–75. doi:10.1016/0891-5849(94)90008-6. PMID 7959167.
  11. Begley TP (2009). Wiley encyclopedia of chemical biology. Hoboken, N.J.: John Wiley & Sons. ISBN 9780471754770. OCLC 243818536.
  12. Ahern K, Rajagopal I, Tan T (2018). Biochemistry Free for All. Creative Commons. p. 432.
  13. Montano-Herrera L, Laycock B, Werker A, Pratt S (March 2017). "The Evolution of Polymer Composition during PHA Accumulation: The Significance of Reducing Equivalents". Bioengineering. 4 (1): 20. doi:10.3390/bioengineering4010020. PMC 5590436. PMID 28952499.
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