Redox potentials of the flavoprotein lactate oxidase

The redox potentials for both electron transfers for the enzyme lactate oxidase have been measured at pH 7.0 in 0.01 M imidazole buffer at 25 degrees C. Methylviologen is the electrochemically generated reducing agent capable of transferring both electrons to the enzyme in this spectroelectrochemical experiment. The E0' values are as follows: for EFlox + e- = EFl-., E0'1 = -0.067 +/- 0.006 V; for EFl-. + e- + H+ = EFlredH-, E0'2 = -0.231 +/- 0.004 V. All potentials are reported vs. the standard hydrogen electrode (SHE). Both electron transfers are reversible. Consistent with the 164-mV potential separation, 95% of the enzyme anion radical is thermodynamically stabilized at half-reduction in all experiments.