Does coenzyme Q10 transfer electrons in the mitochondrial respiratory chain and protect cell membranes from oxidative damage?

Coenzyme Q10 (CoQ10) is an endogenous lipid-soluble quinone with two linked biochemical roles: mitochondrial electron transport and antioxidant activity in lipid environments. Both parts of the claim are strongly supported as mechanisms of CoQ10 biology.

Mitochondrial function

• CoQ10 resides in the inner mitochondrial membrane and cycles between oxidized ubiquinone and reduced ubiquinol.
• It accepts electrons from complex I (NADH-derived) and complex II (succinate-derived), diffuses within the membrane, and delivers electrons to complex III via the Q cycle. This supports downstream cytochrome-c reduction and proton-motive-force generation for ATP synthesis.
• Functional deficiency data corroborate this carrier role: CoQ10-deficient cells show reduced quinone-dependent complex I–III and II–III activity, lower oxygen consumption, impaired proton-motive force, and diminished ATP production; repletion can partly restore respiratory activity.

Antioxidant and membrane effects

• Ubiquinol partitions into phospholipid bilayers, particularly near the polar–lipid interface where lipid oxidation propagates. It donates hydrogen/electrons to lipid-peroxyl radicals, terminating lipid-peroxidation chain reactions that otherwise damage membrane fatty-acyl chains.
• Ubiquinol can also reduce the α-tocopheroxyl radical back to α-tocopherol, potentially sustaining vitamin E’s lipid-phase radical-trapping activity.
• Experimental membrane/liposome findings support this protective chemistry. In human trials, CoQ10 has been associated with lower circulating malondialdehyde, although results are highly heterogeneous; it also increases lipoprotein ubiquinol and LDL resistance to oxidation. These outcomes do not establish the magnitude of protection in particular human cell membranes.

Bottom line

• The claim is scientifically well established: CoQ10 is a central mobile electron carrier between respiratory complexes I/II and III, and its reduced form is a membrane-localized, chain-breaking antioxidant that can protect membrane lipids from oxidative damage. The mechanism is strong; supplementation-specific membrane protection in humans is less precisely quantified.