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Different Q-pools are more or less clearly distinguished in the cell, related to a variety of models describing degress of Q-pool behavior. (1) CoQ-pools are distinguished according to their compartmentation in the cell: mitochondrial CoQ (mtCoQ) and CoQ in other organelles versus plasma-membrane CoQ. (2) The total mitochondrial CoQ-pool mtCoQ is partitioned into an ETS-reactive Q-pool, Qra, and an inactive mtCoQ-pool, Qia. (2a) The Qra-pool is fully reduced in the form of quinol QH2 under anoxia, and fully oxidized in the form of quinone in aerobic mitochondrial preparations incubated without CHNO-fuel substrates. Intermediate redox states of Qra are sensitive to pathway control and coupling control of mitochondrial electron transfer and OXPHOS. (2b) The Qia-pool remains partially reduced and oxidized independent of aerobic-anoxic transitions. The redox state of Qia is insensitive to changes in mitochondrial respiratory states. (3) The Qra-pool is partitioned into Q with Q-pool behavior according to the fluid-state model (synonymous: random-collision model) and Q tightly bound to supercomplexes according to the solid-state model. The two models describe the extremes in a continuum of homogenous or heterogenous Q-pool behavior. The CII-Q-CIII segment of the S-pathway is frequently considered to follow homogenous Q-pool behavior participating in the Qhom-pool, whereas the CI-Q-CIII segment of the N-pathway indicates supercomplex organization and metabolic channeling with different degrees of Q-pool heterogeneity contributing to the Qhet-pool.

Abbreviation: Q

Reference: Komlodi 2021 MitoFit Q

Communicated by Gnaiger Erich 2021-04-03
Q-pool Symbol Definition Balance References
Coenzyme Q CoQ total CoQ in the cell, in mt-preparations, or added experimentally
mitochondrial CoQ mtCoQ total CoQ in mitochondria mtCoQ = Qra + mtCoQia
inactive mtCoQ mtCoQia insensitive to changes in mitochondrial respiratory states; partially oxidized under anoxia and partially reduced in aerobic mt-preparations incubated without CHNO-fuel substrates 1, 2, 3
ETS-reactive Q Qra = Q electron-transfer-system reactive mtCoQ, fully reduced under anoxia, fully oxidized in aerobic mt-preparations incubated without CHNO-fuel substrates Q = Qhom + Qhet 1, 2, 3
homogenous Q Qhom homogenous pool of ETS-reactive Q according to the fluid-state model (random-collision model) 1, 4, 5
heterogenous Q Qhet heterogenous pool of ETS-reactive Q according to the solid-state model 4-7

  1. Kröger A, Klingenberg M (1973) Further evidence for the pool function of ubiquinone as derived from the inhibition of the electron transport by antimycin. Eur J Biochem 39:313-23. - »Bioblast link«
  2. Jørgensen BM, Rasmussen HN, Rasmussen UF (1985) Ubiquinone reduction pattern in pigeon heart mitochondria. Identification of three distinct ubiquinone pools. Biochem J 229:621-9. - »Bioblast link« — A third Q-pool is suggested as an exo-mtCoQ-pool, detected by its reduction by added NADH and located on the outer face of the mtIM.
  3. Van den Bergen CW, Wagner AM, Krab K, Moore AL (1994) The relationship between electron flux and the redox poise of the quinone pool in plant mitochondria. Interplay between quinol-oxidizing and quinone-reducing pathways. Eur J Biochem 226:1071-8. - »Bioblast link«
  4. Gutman M, Silman N (1972) Mutual inhibition between NADH oxidase and succinoxidase activities in respiring submitochondrial particles. FEBS Lett 26:207-10. doi: 10.1016/0014-5793(72)80574-x. - »Bioblast link«
  5. Rich PR (1984) Electron and proton transfers through quinones and cytochrome bc complexes. Biochim Biophys Acta 768:53-79. - »Bioblast link«
  6. Lenaz G, Genova ML (2007) Kinetics of integrated electron transfer in the mitochondrial respiratory chain: random collisions vs. solid state electron channeling. Am J Physiol Cell Physiol 292:C1221-39. doi: 10.1152/ajpcell.00263.2006. - »Bioblast link«
  7. Enriquez JA, Lenaz G (2014) Coenzyme Q and the respiratory chain: coenzyme Q pool and mitochondrial supercomplexes. Mol Syndromol 5:119-40. - »Bioblast link«



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The Q-Module is part of the NextGen-O2k project

The Q-Module allows for monitoring of the redox state of electron transfer-reactive coenzyme Q at the Q-junction using the specific Q-Stoppers with the integrated three-electrode system and the modified electronics of the NextGen-O2k. Cyclic voltammetry is used for quality control and for defining the polarisation voltage applied during Q-redox measurements.
  • Komlódi T, Cardoso LHD, Doerrier C, Moore AL, Rich PR, Gnaiger E (2021) Coupling and pathway control of coenzyme Q redox state and respiration in isolated mitochondria. Bioenerg Commun 2021.3. https://doi.org/10.26124/bec:2021-0003
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