THE EFFECT OF SODIUM-CHLORIDE ON CARBONIC-ANHYDRASE ACTIVITY IN MARINE MICROALGAE

The effects of NaCl on the internal and external carbonic anhydrase (CA) activity of several marine microalgae were studied. Unlike freshwater microalgae in which CA activity is generally inhibited by NaCl, marine microalgae exhibited considerable species-dependent variation when exposed to NaCl. CA activity in Phaeodactylum tricornutum, a diatom, was inhibited, whereas it was activated in the coccolithophorid Pleurochrysis carterae. CA activity in the chlorophyte Dunaliella primolecta was not significantly affected by NaCl. In Dunaliella salina and Dunaliella parva, NaCl inhibited external CA without affecting the internal activity, whereas in Chlorella vulgaris C-133 and Dunaliella peircei only the internal CA was inhibited. Internal CA of Dunaliella tertiolecta was not affected by NaCl, but the external enzyme was significantly enhanced. Salt substitution experiments revealed that chloride (Cl-) is the ion affecting CA activity; the effect of Cl- can be replaced by bromide ion. Cl- affects external CA activity while also affecting the apparent affinity for inorganic carbon during photosynthesis. Microalgae whose internal CA activity was enhanced by Cl- showed higher intracellular Cl- concentrations than those species that were inhibited.