Sodium affects the metabolism of eukaryotes and prokaryotes in several ways. This review collates information on the effects of Na+on the metabolism of cyanobacteria with emphasis on the N2,fixing filamentous species. Na+is required for nitrogenase activity inAnabaena torulosa, AnabaenaL-31 andPlectonema boryanum.The features of this requirement have been mainly studied inAnabaena torulosa.The need for Na+is specific and cannot be replaced by K+, Li+, Ca 2 + or Mg2+. Processes crucial for expression of nitrogenase such as molybdenum uptake, protection of the enzyme from oxygen inactivation and conformational activation of the enzyme are not affected by Na+. Mo-Fe protein and Fe protein, the two components of nitrogenase are synthesized in the absence of Na+but the enzyme complex is catalytically inactive. Photoevolution of O2and CO2fixation, which are severely inhibited in the absence of Na+, are quickly restored by glutamine or glutamate indicating that Na+deprivation affects photosynthesis indirectly due to deficiency in the products of N2fixation. Na+deprivation decreases phosphate uptake, nucleoside phosphate pool and nitrogenase activity. These effects are reversed by the addition of Na+suggesting that a limitation of available ATP caused by reduced phosphate uptake results in loss of nitrogenase activity during Na+starvation.
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