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Background  When cells are exposed to high salinity conditions, they develop a mechanism to extrude excess Na +  from cells to maintain the cytoplasmic Na +  concentration. Until now, the ATPase involved in Na +  transport in cyanobacteria has not been characterized. Here, the characterization of ATPase and its role in Na +  transport of alkaliphilic halotolerant  Aphanothece halophytica  were investigated to understand the survival mechanism of  A. halophytica  under high salinity conditions.    Results  The purified enzyme catalyzed the hydrolysis of ATP in the presence of Na +  but not K + , Li +  and Ca 2+ . The apparent K  m   values for Na +  and ATP were 2.0 and 1.2 mM, respectively. The enzyme is likely the F 1 F 0 -ATPase based on the usual subunit pattern and the protection against  N,N' -dicyclohexylcarbodiimide inhibition of ATPase activity by Na +  in a pH-dependent manner. Proteoliposomes reconstituted with the purified enzyme could take up Na +  upon the addition of ATP. The apparent K  m   values for this uptake were 3.3 and 0.5 mM for Na +  and ATP, respectively. The mechanism of Na +  transport mediated by Na + -stimulated ATPase in  A. halophytica  was revealed. Using acridine orange as a probe, alkalization of the lumen of proteoliposomes reconstituted with Na + -stimulated ATPase was observed upon the addition of ATP with Na +  but not with K + , Li +  and Ca 2+ . The Na + - and ATP-dependent alkalization of the proteoliposome lumen was stimulated by carbonyl cyanide  m  - chlorophenylhydrazone (CCCP) but was inhibited by a permeant anion nitrate. The proteoliposomes showed both ATPase activity and ATP-dependent Na +  uptake activity. The uptake of Na +  was enhanced by CCCP and nitrate. On the other hand, both CCCP and nitrate were shown to dissipate the preformed electric potential generated by Na + -stimulated ATPase of the proteoliposomes.    Conclusion  The data demonstrate that Na + -stimulated ATPase from  A. halophytica , a likely member of F-type ATPase, functions as an electrogenic Na +  pump which transports only Na +  upon hydrolysis of ATP. A secondary event, Na + - and ATP-dependent H +  efflux from proteoliposomes, is driven by the electric potential generated by Na + -stimulated ATPase.

bmc biochemistry

Na+-stimulated ATPase of alkaliphilic halotolerant cyanobacterium Aphanothece halophytica translocates Na+ into proteoliposomes via Na+ uniport mechanism