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 80822-5/asset/equation/feb20014579386808225-math-si1.gif?v=1&s=3a89b956edfc9755c38a868773b53c6a211e5776)
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 80822-5/asset/equation/feb20014579386808225-math-si2.gif?v=1&s=6803ab8680a99858f5735cff8aa1176f04f0cb6a)
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.
