Figure 3.

pH dependence of the rate constants of (i) the electron transfer to Q_B⁻ after the second flash (as measured at 450–480 nm) in the presence (□) and in the absence (⋄) of pH buffer; (ii) the difference voltage transients (as measured at 524 nm) in the presence (▿) and in the absence (▵,▴) of pH buffer; and (iii) pH transients (○,●) with no pH buffer. Open symbols, R. sphaeroides; closed symbols, R. capsulatus. Hepes (2 mM) was added as pH buffer at pH 7.2 with NR as pH indicator. Tris (3 mM) was used as pH buffer with CR at pH 8.1. Other conditions were the same as those described for Fig. 1, except that only 50 mM KCl was added in the presence of pH buffer.