Figure 3.

Effect of various compounds on O₂ evolution and ¹⁴C labeling of subunits in PSII at pH 7.5. The incubation time with the ¹⁴C-labeled amine was 30 min. In some cases, the error bars are smaller than the symbols used to represent the data. In A, solid diamonds, the O₂ evolution activity of PSII-2 at pH 7.5 was measured as a function of added NaCl. Sample buffer contained: 0.4 M sucrose/50 mM Hepes-NaOH, pH 7.5/10 mM Ca(OH)₂/1 mM potassium ferricyanide/0.25 mM recrystallized 2,6-dichlorobenzoquinone. The maximum (100%) corresponds to 350 μmol O₂ (mg Chl-hr)⁻¹. In A, open squares, the amount of ¹⁴C bound to CP47 in PSII-2 was measured as a function of added NaCl. Samples were incubated with 0.19 mM [¹⁴C]benzylamine-hydrochloride (free base concentration, 2.8 μM). In B, the amount of bound ¹⁴C was measured as a function of added NaCl. PSII-2 was incubated with 4 mM [¹⁴C]methylamine-hydrochloride (free base concentration, 2.8 μM). Because [¹⁴C]methylamine was only available as the hydrochloride, the first data point was obtained at 4 mM Cl⁻. Data shows labeling of CP47 (open squares), MSP (open triangles), and the D2/D1 polypeptides (solid circles). In B, the amount of bound ¹⁴C in CP47 was also measured as a function of added sodium sulfate after incubation of PSII-2 with 4 mM [¹⁴C]methylamine-hydrochloride (solid squares). MSP and the D2/D1 polypeptides behaved similarly on the addition of sodium sulfate (data not shown). In C and D, the amount of bound ¹⁴C from 4 mM [¹⁴C]methylamine-hydrochloride was measured as a function of added (unlabeled) Tris and dimethylamine, respectively. Data shows labeling of CP47 (open squares), MSP (open triangles), and the D2/D1 polypeptides (solid circles) in PSII-2. Data in C also shows the Tris competition with labeling of CP47 (solid squares) and the D2/D1 (open circles) polypeptides in PSII-3.