FIGURE 5.

Proton efflux from BtSMPs drives sodium ion uptake by deactive BtCI (Experiment B). A, BtSMPs were placed into buffer containing 10 mm Tris-SO₄, 80 mm ChCl, 250 mm sucrose, pH 7.5, and 0.25 μm ACMA. The active/deactive status of complex I (A- or D-form) was set beforehand (see “Experimental Procedures”). Each trace is the average from at least three experiments, with the standard deviations indicated by shading. 1 mm succinate, 5 mm Na₂SO₄, 0.5 mm KCN, and 2 μg ml⁻¹ monensin were added as indicated. 200 nm rotenone was added along with the Na₂SO₄ and KCN where indicated. The signal has been normalized to 100% at the end of the experiment (to compare the traces during the recovery phase) and to 0% before the addition of M⁺ and cyanide (where M⁺ = Li⁺, Na⁺, K⁺, or Rb⁺); ∼60% of the total fluorescence was quenchable. B, same as A except with 5 mm K₂SO₄ instead of 5 mm Na₂SO₄. Conditions are: 21 °C, ∼30 μg ml⁻¹ protein.