Fig. 6

Na⁺ dependence of ferredoxin:NAD oxidoreductase (FNO) activity as catalyzed by the purified Rnf complex. Dependence of FNO activity on different concentrations of NaCl (■), KCl (▼), or LiCl (▲) was measured in anoxic cuvettes containing Na⁺-free buffer (20 mM Tris–HCl, pH 7.7, 2 mM DTE, 4 µM resazurin; contaminating Na⁺ concentration: 0.125 µM Na⁺) under a CO atmosphere with a pressure of 0.5 × 10⁵ Pa. 10 µl ferredoxin (3 mM), 5 µl carbon monoxide dehydrogenase (CODH; 30 mg/ml), and 14 µg of the Rnf complex were added. The reaction was started by addition of 30 µl NAD⁺ (100 mM) and reduction of NAD⁺ at 340 nm was measured. Data points represent two replicates