Increased levels of cytochrome oxidase and sodium‐proton antiporter in the plasma membrane of Anacystis nidulans after growth in sodium‐enriched media

Typical rates of horse heart ferrocytochrome c oxidation by purified plasma membrane preparations of the cyanobacterium Anacystis nidulans after one week of growth at low (0.03 M) and high (0.4–0.5 M) Na+ concentrations were 15 and 170 per mg protein, respectively. Virtually no change was observed in the cytochrome oxidase activity of isolated and purified thylakoid membranes (approx. 3–5 nmol cyt per mg protein irrespective of Na+ concentration during growth). Concomitantly, the rate of whole cell respiration (oxygen uptake) and the capacity for Na+/H+ exchange (per mg dry wt cells) by 0.4 M NaCl‐grown cells were 7‐ and 5‐fold enhanced, respectively, compared with control cells. The data are in accordance with electron transport‐driven Na+ extrusion from respiring A. nidulans, primarily mediated by the plasma membrane‐bound cytochrome oxidase.