ИСТИНА

Primary Na+- pump, Na+-ATPase, related to the family of P-type cation-translocating ATPases has been demonstrated in the plasma membrane (PM) of marine unicellular green microalga Tetraselmis (Platymonas) viridis [1,2]. The Na+-ATPase supposed to be the principal mechanism driving Na+ extrusion out of the cytosol in this alga. T. viridis can tolerate salinity fluctuation in the wide range of NaCl concentrations. In present study effect of different external salinity on Na+-ATPase was studied using PM vesicles isolated from the alga growing at 50 mM, 500 mM, 900 mM or 1,2 M NaCl in an artificial sea water for at least 7 days (long-term adaptation). Na+-ATPase operation was judged by accompanying intravesicular alkalization detected with the pH indicator pyranine loaded into the vesicles [3]. The dependency of Na+-ATPase activity on sodium concentration showed two-phase kinetics in all PM fractions except vesicles isolated from algae cultured at 50 mM NaCl in the medium. Two-phase kinetics in high-salt preparations suggests existence of either two separate Na+ transporting systems or single one with two binding sites of different affinity for Na+ ions. SDS-PAGE of PM proteins revealed several polypeptides (112, 105, 100 kDa) in the 100 kDa region where phosphointermediate of Na+-ATPase has been found [4]. These polypeptides appeared differently depending on growing conditions. It is hypothesized that new isoforms of Na+-ATPase with different affinity to Na+ appear in T.viridis PM under high salinity.