Modification of redox equilibria between heme and flavin within yeast flavocytochrome b2 (l-lactate cytochrome c reductase) upon binding of pyruvate,the reaction product

Direct determinations of the concentration of semiquinone spin in redox equilibrium with the cytochrome b₂ moiety were carried out at room temperature in the presence of added pyruvate or in its absence. Results show that redox potentials of the one-electron couples of the prosthetic flavin are markedly affected by binding of pyruvate the reaction product in the oxidation of l-lactate. The proportion of flavin semiquinone nearly reaches then 100 per cent.