Figure 6.

Amplitude of the Fd fast-reduction phases (500 ns and 20 μs) as a function of total Fd concentration. ▵, DE PSI; ○, DF PSI; ⋄, DΔCt PSI; and □, D10 PSI. Solid lines represent the fit of the binding equilibrium:

Dotted line is the fit for a WT PSI. Inset, Kinetics of flash-induced Fd reduction by PSI measured at 580 nm. Measurements were made in square 1-cm cuvettes containing 0.2 μm PSI, 20 mm Tricine/NaOH, pH 8.0, 30 mm NaCl, 5 mm MgCl₂, 10 μm DCPIP, 2 mm Asc, and 0.03% (w/v) β-DM. Each trace is the average of 64 experiments recorded in the presence and in the absence of Fd. For each trace, total Fd concentration was [Fd] = 2 × K_D, allowing direct comparison of the kinetics. Trace a, D10 PSI and 2 μm Fd (2 × K_D). Trace b, WT PSI and 0.4 μm Fd (2 × K_D).