Figure 4.

Stability of BR and cytochrome b₆f complexed by amphipols. (A) BR was either kept in 10 mM OTG in 100 mM AP, pH 8.0 (□; final concentration of OTG was 10 mM), or complexed by A8-75 (○) or A8-35 (•) as described in the legend of Fig. 2B (final concentration of amphipol was 0.5 g/liter). The three samples were stored at 4°C in the dark. Every second or third day, each sample was centrifuged in the Airfuge (cf. legend to Fig. 2) before measuring the absorbance at 546 nm. (B) Cytochrome b₆f was either kept in 20 mM HG, 0.1 g/liter EPC, 400 mM AP (pH 8.0) (▪), or complexed with A8-75 (▵) or A8-35 (▴) and isolated by sucrose gradient centrifugation as described in the legend of Fig. 3. The samples were stored at 4°C in the dark. Enzymatic activity was determined by diluting an aliquot 50- to 200-fold in 0.25 mM LM, 20 mM Tricine·NaOH buffer (pH 8.0), and measuring the rate of stigmatellin-sensitive electron transfer from decylplastoquinol to oxidized plastocyanin (14).