Q-redox state

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Q-redox state

Description

The Q-redox state reflects the redox status of the Q-junction in the mitochondrial or chloroplast electron transfer system (ETS). Coenzyme Q (CoQ or Q, ubiquinone) is a mobile redox component located centrally in the mitochondrial ETS, while plastoquinones are essential mobile components in the photosynthetic system with a similar function. The Q-redox state depends on the balance between reducing capacities of convergent electron entries from fuel substrates into the Q-junction and oxidative capacities downstream of Q to the electron acceptor oxygen. Therefore, deficiencies in the mitochondrial ETS, originating from e.g. the malfunction of respiratory Complexes, can be detected by measuring the changes of the Q-redox state with respect to the respiratory activity.

A three-electrode system was implemented into the NextGen-O2k to monitor the Q-redox state continuously and simultaneously with respiratory oxygen consumption. Added CoQ2 reflects the mitochondrial Q-redox state when equilibrating both with the detecting electrode and the biological sites (e.g. Complexes I, II and III).

Communicated by Komlodi T, Cardoso LHD (last update 2021-02-09)

Calculation of the Q-redox fractions

The Q-redox state is expressed as the fraction of reduced Q (Qr) in each steady state of a SUIT protocol. In order to calculate the reduced Q fraction, the raw Q signal (Uraw) is calibrated against the fully oxidized Q signal (Uox) and the fully reduced Q signal (Ured). Uox is measured in the presence of CoQ2 and isolated mitochondria. The CI inhibitor rotenone might have to be added to inhibit respiration of endogenous substrates. Ured is determined under anoxia after the sample consumed the accessible O2 in the O2k-chamber. Qr is calculated as a proportion of the fully reduced Q. The sum of the oxidized and reduced fractions of Q equals 1, Qr+Qox = 1. In this formalism the intermediate redox state of semiquinone is not taken into account.
Further details: Komlodi 2021 MitoFit Q

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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.
Reference:
  • 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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