Figure 2. Fd_red:NAD⁺ oxidoreductase activity of membranes of C. ljungdahlii as a function of Na⁺ concentration (A) and of inverted membrane vesicles in the presence of different ionophores (B).

Fno activity was measured in anoxic cuvettes filled with 1 ml 20 mM Tris (sodium free)-HCl buffer (pH 7.7) containing 2 mM DTE and 2 μM resazurin at a pressure of 0.5 × 10⁵ Pa CO. NaCl was added to the concentration indicated. Ferredoxin (30 μM), Acs/CODH (30 μg/ml), and washed membranes or inverted membrane vesicles (150 μg/ml) were added. If indicated, the ionophores ETH2120 or TCS were added at a concentration of 10 μM. The reaction was started by addition of NAD⁺ (4 mM). Formation of NADH was measured at 340 nm.