Figure 4.

Light-induced absorption changes at 460 nm after a laser flash in RC crystals with and without Cd²⁺. Each trace is an average of 40 flashes. The absorbance change is associated with electron transfer from Q_A⨪ to Q_B (Q_A⨪Q_B → Q_AQ_B⨪). Crystals were placed between two sealed coverslips in artificial mother liquor without and with 10 mM Cd²⁺. The solid lines represent fits to a biexponential function with rate constants k₁ = 6000 s⁻¹ and k₂ = 800 s⁻¹. The rate constant and the increase in amplitude of the slower phase in the presence of Cd²⁺ are similar to those measured in solution (not shown), showing that the binding site in the crystal is the same as in solution.