Q-redox state: Difference between revisions

Revision as of 13:28, 9 February 2021

high-resolution terminology - matching measurements at high-resolution

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). Ubiquinones, also known as coenzyme Q, and plastoquinones are essential mobile components of the mitochondria and chloroplasts that transfer electrons between the respiratory or photosynthetic complexes of the ETS. The Q redox state is dependent on the relative activities of the ETS enzymes that reduce and oxidize the quinones. 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 respiratory activity.

Abbreviation: Q_r/Q_t

Calculation of the Q redox fractions (in preparation)

The Q redox state is expressed as the fraction of reduced Q (Q_r) 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 (U_ox) and the fully reduced Q signal (U_red). U_ox 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. U_red is determined under anoxia after the sample consumed the accessible O₂ in the O2k-chamber. Q_r is calculated as a proportion of the fully reduced Q (Table 1). The sum of the oxidized and reduced fractions of Q equals 1, Q_r+Q_ox = 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

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 polarization 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

Communicated by Komlodi T, Cardoso LHD 2020-07-28

Bioblast links: Q - >>>>>>> - Click on [Expand] or [Collapse] - >>>>>>>

Coenzyme Q

» Coenzyme Q

» Quinone, Ubiquinone Q; oxidized

» Quinol, Ubiquinol QH₂; reduced

» Semiquinone

» Coenzyme Q2

» Q-redox state

» Q-pools

Mitochondrial pathways, respiratory Complexes, and Q

» Q-cycle

» Q-junction

» Convergent electron flow

» NS-pathway

» FNS

» FNSGp

» N-pathway

» Reverse electron flow from CII to CI

» CI

» Rotenone

» Amytal

» Piericidin

» S-pathway

» CII

» Malonate

» F-pathway

» CETF, Electron-transferring flavoprotein complex

» Gp-pathway

» CGpDH, Glycerophosphate dehydrogenase complex

» CIII

» Myxothiazol

» Choline dehydrogenase

» Dihydro-orotate dehydrogenase

NextGen-O2k and Q-Module

» NextGen-O2k

» Q-Module

» Q-Sensor

» Cyclic voltammetry

» Three-electrode system

General

» Categories of SUIT protocols

» Electron transfer pathway

» Electron-transfer-pathway state

» F-junction

» N-junction

@@ Line 6: / Line 6: @@
 == Calculation of the Q redox fractions (''in preparation'') ==
-To analyze the Q redox state, [[SUIT]] protocols are designed with one step in which the [[Q]] is fully reduced and one in which it is fully oxidized. The values obtained will be used to calculate the Q redox ratios.
+The Q redox state is expressed as the fraction of reduced Q (Q<sub>r</sub>) 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 (''U''<sub>ox</sub>) and the fully reduced Q signal (''U''<sub>red</sub>). ''U''<sub>ox</sub> 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. ''U''<sub>red</sub> is determined under anoxia after the sample consumed the accessible O<sub>2</sub> in the O2k-chamber. ''Q''<sub>r</sub> is calculated as a proportion of the fully reduced Q (Table 1). The sum of the oxidized and reduced fractions of Q equals 1, ''Q''<sub>r</sub>+''Q''<sub>ox</sub> = 1. In this formalism the intermediate redox state of semiquinone is not taken into account.
-First, the signal is corrected for the fully oxidized Q state (Q<sub>ox</sub>), which can be measured, ''e.g.'' in the presence of [[Isolated mitochondria |isolated mitochondria]] and CoQ2. (To fully oxidize the Q-pool rotenone can be added which inhibits respiration of endogenous substrates. However, it cannot be applied when NADH- or F-linked O<sub>2</sub> flux is measured). Q<sub>ox</sub> is then subtracted from the raw Q signal for every step before the calculation of the ratios:
-::: Q<sub>r</sub> = Q<sub>raw</sub>-Q<sub>ox</sub>
-Then, the Q redox ratio is calculated between the given Q-signal in the presence of different substrates/inhibitors/uncouplers (Q<sub>r</sub>) and the fully reduced Q state (Q<sub>t</sub>, also corrected for Q<sub>ox</sub>), which can be detected under anoxia for isolated mitochondria:
-::: Q<sub>r</sub>/Q<sub>t</sub>
 == The [[Q-Module]] is part of the [[NextGen-O2k]] project==
 {{Template:Q-Module}}