ETQ-QO links the oxidation of fatty acids and some amino acids to oxidative phosphorylation in the mitochondria. Specifically, it catalyzes the transfer of electrons from electron transferring flavoprotein (ETF) to ubiquinone, reducing it to ubiquinol. The entire sequence of transfer reactions is as follows:
Acyl-CoA → Acyl-CoA dehydrogenase → ETF → ETF-QO → UQ → Complex III.