Coupling and pathway control of coenzyme Q redox state and respiration in isolated mitochondria

Abstract

Redox states of the mitochondrial coenzyme Q pool, which reacts with the electron transfer system, reflect the balance between (1) reducing capacities of electron flow from fuel substrates converging at the Q-junction, (2) oxidative capacities downstream of Q to O₂, and (3) the load on the OXPHOS system utilizing or dissipating the protonmotive force.

A three-electrode sensor (Rich 1988; Moore et al 1988) was implemented into the NextGen-O2k to monitor continuously the redox state of CoQ₂ added as a Q-mimetic simultaneously with O₂ consumption. The Q-Module was optimized for high signal-to-noise ratio, minimum drift, and minimum oxygen diffusion. CoQ₂ equilibrates in the same manner as Q at Complexes CI, CII and CIII. The CoQ₂ redox state is monitored amperometrically with the working electrode, which is poised at CoQ₂ redox peak potentials determined by cyclic voltammetry. The voltammogram also provides quality control of the Q-sensor and reveals chemical interferences.

 The CoQ₂ redox state and O₂ consumption were measured simultaneously in isolated mouse cardiac and brain mitochondria. CoQ₂ ― and by implication mitochondrial Q ― was more oxidized when O₂ flux was stimulated by coupling control: when energy demand increased from LEAK to OXPHOS and electron transfer capacities in the succinate pathway. In contrast, CoQ₂ was more reduced when O₂ flux was stimulated by pathway-control of electron input capacities, increasing from the NADH (N)- to succinate (S)-linked pathway which converge at the Q-junction, with CI-Q-CIII and CII-Q-CIII segments, respectively. N- and S- respiratory pathway capacities were not completely additive, compatible with partitioning of Q intermediary between the solid-state and liquid-state models of supercomplex organization. The direct proportionality of CoQ₂ reduction and electron input capacities through the CI-Q-CIII and CII-Q-CIII segments suggests that CoQ₂ is accurately mimicking mitochondrial Q-redox changes.

Cite:

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