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 enzymes (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 CoQ redox state when equilibrating both with the detecting electrode and the biological sites (Complexes I, II and III).
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.
The Q-Module is part of the NextGen-O2k project
In the NextGen-O2k project we are working on developing the Q-Module for the new series of our O2k-FluoRespirometer, the NextGen-O2k. The Q-Module allows us to monitor the Q redox state of the Q-junction using the specific Q-Stoppers with the integrated three-electrode system and the modified electronics inside the O2k housing.
Communicated by Komlodi T, Cardoso LHD (last update 2021-02-09)
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