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'''Reverse electron flow''' (also known as '''reverse electron transport''') is a mechanism in [[microbial metabolism]]. [[Chemolithotroph]]s using an [[electron donor]] with a higher [[redox potential]] than [[NADP|NAD(P)<sup>+</sup>/NAD(P)H]], such as nitrite or sulfur compounds, must use energy to reduce NAD(P)<sup>+</sup>. This energy is supplied by consuming [[proton motive force]] to drive electrons in a reverse direction through an [[electron transport chain]] and is thus the reverse process as forward electron transport. In some cases, the energy consumed in reverse electron transport is five times greater than energy gained from the forward process.<ref>{{cite book | last1=Kim | first1=B. H. |author2-link=Geoffrey Michael Gadd | last2=Gadd | first2=G. M. | year=2008 | title=Bacterial Physiology and Metabolism | url=https://archive.org/details/bacterialphysiol0000kimb | url-access=registration | publisher=Cambridge University Press | location=Cambridge, UK }}</ref> [[Autotroph]]s can use this process to supply reducing power for inorganic [[carbon fixation]].
'''Reverse electron flow''' (also known as '''reverse electron transport''') is a mechanism in [[microbial metabolism]]. [[Chemolithotroph]]s using an [[electron donor]] with a higher [[redox potential]] than [[NADP|NAD(P)<sup>+</sup>/NAD(P)H]], such as nitrite or sulfur compounds, must use energy to reduce NAD(P)<sup>+</sup>. This energy is supplied by consuming [[proton motive force]] to drive electrons in a reverse direction through an [[electron transport chain]] and is thus the reverse process as forward electron transport. In some cases, the energy consumed in reverse electron transport is five times greater than energy gained from the forward process.<ref>{{cite book | last1=Kim | first1=B. H. |author2-link=Geoffrey Michael Gadd | last2=Gadd | first2=G. M. | year=2008 | title=Bacterial Physiology and Metabolism | url=https://archive.org/details/bacterialphysiol0000kimb | url-access=registration | publisher=Cambridge University Press | location=Cambridge, UK }}</ref> [[Autotroph]]s can use this process to supply reducing power for inorganic [[carbon fixation]].


'''Reverse electron transfer''' ('''RET''') is the process that can occur in respiring [[mitochondria]], when a small fraction of electrons from [[reduced]] [[ubiquinol]] is driven upstream by the [[membrane potential]] towards to [[mitochondrial complex I]]. This result in [[reduction]] of [[oxidized]] pyridine nucleotide ([[NAD]]<sup>+</sup> or [[NADP]]<sup>+</sup>). This is a reversal of [[exergonic]] reaction of forward [[electron transfer]] in the mitochondrial complex I when electrons travel from [[NADH]] to [[ubiquinone]].
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==References==

==Mechanism==
The term "Reverse electron transfer" is used in regard to the reversibility of the reaction performed by complex I of the mitochondrial or bacterial [[respiratory chain]]. [[Complex I]] is responsible for the [[oxidation]] of [[NADH]] generated in [[catabolism]] when in the ''forward'' reaction electrons from the nucleotide (NADH) are transferred to membrane [[ubiquinone]] and energy is saved in the form of [[proton-motive force]]. The reversibility of the electron transfer reactions at complex I was first discovered when [[Britton Chance|Chance]] and Hollunger have shown that the addition of [[succinate]] to mitochondria in State 4 leads to an [[uncoupler]]-sensitive reduction of the intramitochondrial nucleotides (NAD(P)<sup>+</sup>).<ref>{{cite journal |last1=Chance |first1=Britton |author-link1=Britton Chance |last2=Hollunger |first2=Gunnar |title=Energy-Linked Reduction of Mitochondrial Pyridine Nucleotide |journal=Nature |date=March 1960 |volume=185 |issue=4714 |pages=666–672 |doi=10.1038/185666a0|pmid=13809106 |bibcode=1960Natur.185..666C |s2cid=4267386 }}</ref>. When succinate is oxidized by intact mitochondria, complex I can [[catalyze]] ''reverse'' electron transfer when a electrons from [[ubiquinol]] (QH<sub>2</sub>, formed during oxidation of succinate) is driven by the proton-motive force to complex I flavin toward the nucleotide-binding site.

Since the discovery of the reverse electon transfer in the 60s' it was regarded as in vitro phenomenon, until the role of RET in the development of [[ischemia]]/[[reperfusion]] injury has been recognized in the brain<ref>{{cite journal |last1=Niatsetskaya |first1=Z. V. |last2=Sosunov |first2=S. A. |last3=Matsiukevich |first3=D. |last4=Utkina-Sosunova |first4=I. V. |last5=Ratner |first5=V. I. |last6=Starkov |first6=A. A. |last7=Ten |first7=V. S. |title=The Oxygen Free Radicals Originating from Mitochondrial Complex I Contribute to Oxidative Brain Injury Following Hypoxia-Ischemia in Neonatal Mice |journal=Journal of Neuroscience |date=2012-02-29 |volume=32 |issue=9 |pages=3235–3244 |doi=10.1523/JNEUROSCI.6303-11.2012|pmid=22378894 |pmc=3296485 }}</ref> and heart.<ref>{{cite journal |last1=Chouchani |first1=Edward T. |last2=Pell |first2=Victoria R. |last3=Gaude |first3=Edoardo |last4=Aksentijević |first4=Dunja |last5=Sundier |first5=Stephanie Y. |last6=Robb |first6=Ellen L. |last7=Logan |first7=Angela |last8=Nadtochiy |first8=Sergiy M. |last9=Ord |first9=Emily N. J. |last10=Smith |first10=Anthony C. |last11=Eyassu |first11=Filmon |last12=Shirley |first12=Rachel |last13=Hu |first13=Chou-Hui |last14=Dare |first14=Anna J. |last15=James |first15=Andrew M. |last16=Rogatti |first16=Sebastian |last17=Hartley |first17=Richard C. |last18=Eaton |first18=Simon |last19=Costa |first19=Ana S. H. |last20=Brookes |first20=Paul S. |last21=Davidson |first21=Sean M. |last22=Duchen |first22=Michael R. |last23=Saeb-Parsy |first23=Kourosh |last24=Shattock |first24=Michael J. |last25=Robinson |first25=Alan J. |last26=Work |first26=Lorraine M. |last27=Frezza |first27=Christian |last28=Krieg |first28=Thomas |last29=Murphy |first29=Michael P. |title=Ischaemic accumulation of succinate controls reperfusion injury through mitochondrial ROS |journal=Nature |date=2014-11-20 |volume=515 |issue=7527 |pages=431–435 |doi=10.1038/nature13909|pmid=25383517 |pmc=4255242 |bibcode=2014Natur.515..431C }}</ref> During ischemia substantial amount of succinate is generated in cerebral<ref>{{cite journal |last1=Sahni |first1=PV |last2=Zhang |first2=J |last3=Sosunov |first3=S |last4=Galkin |first4=A |last5=Niatsetskaya |first5=Z |last6=Starkov |first6=A |last7=Brookes |first7=PS |last8=Ten |first8=VS |title=Krebs cycle metabolites and preferential succinate oxidation following neonatal hypoxic-ischemic brain injury in mice. |journal=Pediatric research |date=2018 |volume=83 |issue=2 |pages=491-497 |doi=10.1038/pr.2017.277 |pmid=29211056}}</ref> or cardiac tissue<ref>{{cite journal |last1=Pisarenko |first1=O |last2=Studneva |first2=I |last3=Khlopkov |first3=V |title=Metabolism of the tricarboxylic acid cycle intermediates and related amino acids in ischemic guinea pig heart. |journal=Biomedica biochimica acta |date=1987 |volume=46 |issue=8-9 |pages=568-571 |pmid=2893608}}</ref> and upon reperfusion it can be oxidized by mitochondria initiating reverse electron transfer reaction. Reverse electron transfer supports the highest rate of mitochondrial Reactive Oxygen Species ([[ROS]]) production, and complex I [[flavin mononucleotide]] (FMN) has been identified as the site where one-electon reduction of oxygen takes place. <ref>{{cite journal |last1=Andreyev |first1=A. Yu. |last2=Kushnareva |first2=Yu. E. |last3=Starkov |first3=A. A. |title=Mitochondrial metabolism of reactive oxygen species |journal=Biochemistry (Moscow) |date=2005 |volume=70 |issue=2 |pages=200–214 |doi=10.1007/s10541-005-0102-7|pmid=15807660 |s2cid=17871230 }}</ref><ref>{{cite journal |last1=Quinlan |first1=Casey L. |last2=Perevoshchikova |first2=Irina V. |last3=Hey-Mogensen |first3=Martin |last4=Orr |first4=Adam L. |last5=Brand |first5=Martin D. |title=Sites of reactive oxygen species generation by mitochondria oxidizing different substrates |journal=Redox Biology |date=2013 |volume=1 |issue=1 |pages=304–312 |doi=10.1016/j.redox.2013.04.005|pmid=24024165 |pmc=3757699 }}</ref><ref>{{cite journal |last1=Stepanova |first1=Anna |last2=Kahl |first2=Anja |last3=Konrad |first3=Csaba |last4=Ten |first4=Vadim |last5=Starkov |first5=Anatoly S |last6=Galkin |first6=Alexander |title=Reverse electron transfer results in a loss of flavin from mitochondrial complex I: Potential mechanism for brain ischemia reperfusion injury |journal=Journal of Cerebral Blood Flow & Metabolism |date=December 2017 |volume=37 |issue=12 |pages=3649–3658 |doi=10.1177/0271678X17730242|pmid=28914132 |pmc=5718331 }}</ref>

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== References ==

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[[Category:Metabolism]]
[[Category:Metabolism]]

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Revision as of 22:26, 19 September 2021

Reverse electron flow (also known as reverse electron transport) is a mechanism in microbial metabolism. Chemolithotrophs using an electron donor with a higher redox potential than NAD(P)+/NAD(P)H, such as nitrite or sulfur compounds, must use energy to reduce NAD(P)+. This energy is supplied by consuming proton motive force to drive electrons in a reverse direction through an electron transport chain and is thus the reverse process as forward electron transport. In some cases, the energy consumed in reverse electron transport is five times greater than energy gained from the forward process.[1] Autotrophs can use this process to supply reducing power for inorganic carbon fixation.

Reverse electron transfer (RET) is the process that can occur in respiring mitochondria, when a small fraction of electrons from reduced ubiquinol is driven upstream by the membrane potential towards to mitochondrial complex I. This result in reduction of oxidized pyridine nucleotide (NAD+ or NADP+). This is a reversal of exergonic reaction of forward electron transfer in the mitochondrial complex I when electrons travel from NADH to ubiquinone.

Mechanism

The term "Reverse electron transfer" is used in regard to the reversibility of the reaction performed by complex I of the mitochondrial or bacterial respiratory chain. Complex I is responsible for the oxidation of NADH generated in catabolism when in the forward reaction electrons from the nucleotide (NADH) are transferred to membrane ubiquinone and energy is saved in the form of proton-motive force. The reversibility of the electron transfer reactions at complex I was first discovered when Chance and Hollunger have shown that the addition of succinate to mitochondria in State 4 leads to an uncoupler-sensitive reduction of the intramitochondrial nucleotides (NAD(P)+).[2]. When succinate is oxidized by intact mitochondria, complex I can catalyze reverse electron transfer when a electrons from ubiquinol (QH2, formed during oxidation of succinate) is driven by the proton-motive force to complex I flavin toward the nucleotide-binding site.

Since the discovery of the reverse electon transfer in the 60s' it was regarded as in vitro phenomenon, until the role of RET in the development of ischemia/reperfusion injury has been recognized in the brain[3] and heart.[4] During ischemia substantial amount of succinate is generated in cerebral[5] or cardiac tissue[6] and upon reperfusion it can be oxidized by mitochondria initiating reverse electron transfer reaction. Reverse electron transfer supports the highest rate of mitochondrial Reactive Oxygen Species (ROS) production, and complex I flavin mononucleotide (FMN) has been identified as the site where one-electon reduction of oxygen takes place. [7][8][9]

References

  1. ^ Kim, B. H.; Gadd, G. M. (2008). Bacterial Physiology and Metabolism. Cambridge, UK: Cambridge University Press.
  2. ^ Chance, Britton; Hollunger, Gunnar (March 1960). "Energy-Linked Reduction of Mitochondrial Pyridine Nucleotide". Nature. 185 (4714): 666–672. Bibcode:1960Natur.185..666C. doi:10.1038/185666a0. PMID 13809106. S2CID 4267386.
  3. ^ Niatsetskaya, Z. V.; Sosunov, S. A.; Matsiukevich, D.; Utkina-Sosunova, I. V.; Ratner, V. I.; Starkov, A. A.; Ten, V. S. (2012-02-29). "The Oxygen Free Radicals Originating from Mitochondrial Complex I Contribute to Oxidative Brain Injury Following Hypoxia-Ischemia in Neonatal Mice". Journal of Neuroscience. 32 (9): 3235–3244. doi:10.1523/JNEUROSCI.6303-11.2012. PMC 3296485. PMID 22378894.
  4. ^ Chouchani, Edward T.; Pell, Victoria R.; Gaude, Edoardo; Aksentijević, Dunja; Sundier, Stephanie Y.; Robb, Ellen L.; Logan, Angela; Nadtochiy, Sergiy M.; Ord, Emily N. J.; Smith, Anthony C.; Eyassu, Filmon; Shirley, Rachel; Hu, Chou-Hui; Dare, Anna J.; James, Andrew M.; Rogatti, Sebastian; Hartley, Richard C.; Eaton, Simon; Costa, Ana S. H.; Brookes, Paul S.; Davidson, Sean M.; Duchen, Michael R.; Saeb-Parsy, Kourosh; Shattock, Michael J.; Robinson, Alan J.; Work, Lorraine M.; Frezza, Christian; Krieg, Thomas; Murphy, Michael P. (2014-11-20). "Ischaemic accumulation of succinate controls reperfusion injury through mitochondrial ROS". Nature. 515 (7527): 431–435. Bibcode:2014Natur.515..431C. doi:10.1038/nature13909. PMC 4255242. PMID 25383517.
  5. ^ Sahni, PV; Zhang, J; Sosunov, S; Galkin, A; Niatsetskaya, Z; Starkov, A; Brookes, PS; Ten, VS (2018). "Krebs cycle metabolites and preferential succinate oxidation following neonatal hypoxic-ischemic brain injury in mice". Pediatric research. 83 (2): 491–497. doi:10.1038/pr.2017.277. PMID 29211056.
  6. ^ Pisarenko, O; Studneva, I; Khlopkov, V (1987). "Metabolism of the tricarboxylic acid cycle intermediates and related amino acids in ischemic guinea pig heart". Biomedica biochimica acta. 46 (8–9): 568–571. PMID 2893608.
  7. ^ Andreyev, A. Yu.; Kushnareva, Yu. E.; Starkov, A. A. (2005). "Mitochondrial metabolism of reactive oxygen species". Biochemistry (Moscow). 70 (2): 200–214. doi:10.1007/s10541-005-0102-7. PMID 15807660. S2CID 17871230.
  8. ^ Quinlan, Casey L.; Perevoshchikova, Irina V.; Hey-Mogensen, Martin; Orr, Adam L.; Brand, Martin D. (2013). "Sites of reactive oxygen species generation by mitochondria oxidizing different substrates". Redox Biology. 1 (1): 304–312. doi:10.1016/j.redox.2013.04.005. PMC 3757699. PMID 24024165.
  9. ^ Stepanova, Anna; Kahl, Anja; Konrad, Csaba; Ten, Vadim; Starkov, Anatoly S; Galkin, Alexander (December 2017). "Reverse electron transfer results in a loss of flavin from mitochondrial complex I: Potential mechanism for brain ischemia reperfusion injury". Journal of Cerebral Blood Flow & Metabolism. 37 (12): 3649–3658. doi:10.1177/0271678X17730242. PMC 5718331. PMID 28914132.
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