Fig. 2.

Two-dimensional analysis of [Cl⁻] and pH dependence of photoassembly. All samples contained 0.25 mM 2-(N-morpholino)ethanesulfonic acid (pH 5.5 to 7.0), 40 mM CaCl₂, 0.16 mM MnCl₂, 8 mM NaHCO₃, 400 mM sucrose, 10 μM dichlorophenolindophenol (DCIP), and 0.25 mg/mL chlorophyll as apo-OEC PSII membranes. Variable concentrations of NaCl were added to control [Cl⁻]. Photoassembly was performed at 50 μE⋅m⁻²⋅s⁻¹ for 20 min. Dots represent the 24 buffer combinations used to generate the plot (pH values of 5.5, 6.0, 6.5, and 7.0, and chloride concentrations of 100, 200, 300, 500, 750, and 1,000 mM). Yields were normalized to the rate of extrinsics-depleted PSII membranes under identical measurement conditions [44.1 μmol of O₂ (mg Chl)⁻¹⋅h⁻¹; SI Appendix, Table S1].