Figure 2.

Optical absorbance changes at 865 nm for native RCs in the presence of cyt c₂²⁺ after two laser flashes spaced Δt apart. Laser flash artifacts are truncated. The ratio of ΔA₂ to ΔA_{No cyt} gives the fraction of photoactive RCs at the time of the second flash (see Eq. 3). ΔA₁ is due to the fraction of RCs that do not have a bound cyt c₂²⁺. Addition of terbutryne to inhibit electron transfer to Q_B eliminated the absorbance change in response to the second laser flash. (Conditions: 3 μM 2.4.1 RCs with Q₁₀ reconstituted into the Q_A and Q_B sites by addition of Q₁₀ in LDAO. After reconstitution, LDAO was 0.03%. 100 μM cyt c₂²⁺, 5 μM ascorbate, 1 mM Tris, and 0.04% maltoside; spectral bandwidth, 10 nm.)