Figure 1.

H⁺/Q_A⁻ (A) and H⁺/Q_B⁻ (B) proton uptake kinetics in the wild-type (L212E, I), L212Q (II), and L212A (III) mutant RCs. The stoichiometries of proton uptake were calibrated as described in Materials and Methods. Conditions: 50 mM NaCl, 0.03% Triton X-100, <10 mM Tris⋅Cl (pH 7.5), 100 μM ferrocene, 500 μM potassium ferrocyanide, and 40 μM o-cresol red. The H⁺/Q_A⁻ proton uptake measurements were done in the presence of 100 μM terbutryn.