Figure 1.

Optical absorbance changes at 412 nm associated with electron transfer from Q_A^−⋅ to Q_B in hybrid (Me₃NQ^−⋅ or MQ_P^−⋅ in the Q_A site and Q₁₀ in the Q_B site) and native (Q₁₀ in both Q_A and Q_B sites) RCs. In native RCs, the absorbance change is due to an electrochromic shift of the BPhe absorption. In hybrid RCs, the main effect is caused by the difference in extinction coefficient between the naphthosemiquinones (NQ^−⋅ in the Q_A site and Q₁₀^−⋅ in the Q_B site). The observed transients in hybrid RCs are reduced by the electrochromic shift, which was assumed to be the same as that observed in native RCs. The data for the hybrid RCs were normalized to the expected absorption determined from the known difference in extinction coefficients between (NQ)_A^−⋅ and Q₁₀^−⋅ (11, 20, 21). A shallow slope determined by monitoring the recombination reactions (D⁺Q_A^−⋅ → DQ_A and D⁺Q_AQ_B^−⋅ → DQ_AQ_B) was subtracted for clarity. Addition of terbutryne, which inhibits electron transfer to Q_B, eliminated the transient kinetic phases. [Conditions: 5 μM 2.4.1RCs, BMK buffer (pH = 7.2), 0.03% LDAO. Spectral bandwidth, 10 nm].