The overall reaction catalyzed by ETF-QO is as follows:
ETF-QO(red) + ubiquinone ↔ ETF-QO(ox) + ubiquinol
Enzymatic activity is usually assayed spectrophotometrically by reaction with octanoyl-CoA as the electron donor and ubiquinone-1 as the electron acceptor. The enzyme can also be assayed via disproportionation of ETF semiquinone. Both reactions are below:
Octanoyl-CoA + Q ↔ QH + Oct-2-enoyl-CoA
2 ETF ↔ ETF + ETF