FIGURE 6.

Proton transfer through F₀ as monitored by two pH indicators reporting pH transients from either side of the chromatophore membrane, (A, B) from the n-side (Cresol red, 90 μM, at a wavelength of 575 nm), and (C, D) from the p-side (Neutral red, 26 μM plus 0.3% w/v BSA, at 545 nm). Traces in parts A and C were recorded in the absence, and traces B and D in the presence of the ionophore valinomycin (2 μM). In the latter case the transmembrane voltage was collapsed by the valinomycin-mediated K⁺ current in <3 ms (see Fig. 2). The relaxation of the pH difference was then entirely due to the entropic driving force (ΔpH). The proton release from bc₁ was slower in the presence of valinomycin (compare to traces 2 in Figs. 6 C and 5 D). The medium contained 50 mM KCl, 5 mM MgCl₂, 2 mM K₄[Fe(CN)₆], 2 mM KCN, 5 μM dMF; pH was 7.9. Chromatophore stock was in 5 mM MgCl₂, 50 mM KCl, 10% sucrose. Traces 1 without, and traces 2 with 3 μM oligomycin added; traces 2-1 = difference trace ± oligomycin. Actinic flashes are marked by arrows; black bars correspond to 0.002 pH units.