Modifications of redox equilibria with semiquinone stabilization upon pyruvate binding to L-lactate cytochrome c oxidoreductase (flavocytochrome b2).

Spectral redox titrations of flavin and cytochrome b2 moieties of flavocytochrome b2 were achieved in the absence and in the presence of pyruvate under equilibrium conditions at 18 degrees C; direct measurements of spin flavosemiquinone proportions have been carried out by EPR determinations at the same temperature. Our results show that the equilibria involving flavin are largely affected by the presence of pyruvate; the semiquinone proportion markedly increases almost till unit near half-reduction of cytochrome b2; at 10 mM pyruvate, the dismutation constant, Kdism = (Fs)2/(Fo)*(Fr) increases by a factor greater than or equal to 10.