Fig. 2. Titrations of Q_o-site with myxothiazol.

(A) Fraction (% of change with no inhibitor) of reduced b_H at 20 ms (after 1^st flash) and 50 ms (after 2^nd flash) versus inhibitor concentration. Chromatophores from native and mutant strains of R. sphaeroides were poised at E_h 100 ±10 mV at pH 7.0 and 20 °C. Rates were measured in the presence of antimycin to block oxidation of heme b_H through the Q_i-site, as Q_o-sites were titrated with myxothiazol. Insert shows titration curves expected without (straight line, green) or with (convex curve, black) inter-monomer electron transfer, from simulation (see [26]). (B) Kinetics of reduction of heme b_H (black) and heme b_L (red) in wild-type following two flashes. Myxothiazol was added at the concentrations shown. The vertical arrows indicate flash activation. The pattern is diagnostic of monomeric function.