Presence of Na⁺-Stimulated P-Type ATPase in the Membrane of a Facultatively Anaerobic Alkaliphile, Exiguobacterium aurantiacum

Abstract.

It was found that a facultatively anaerobic alkaliphile, Exiguobacterium aurantiacum, possesses a membrane-bound ATPase, which was activated specifically by Na⁺. The Na⁺-stimulated ATPase activity reached a maximum value at 200 mM NaCl. In the presence of 200 mM NaCl, the activity was drastically reduced by vanadate, a potent inhibitor of P-type ATPase, with a half-maximal inhibition at 1 μM. Incubation of the membranes with [γ-³²P]ATP followed by acidic lithium dodecyl sulfate–polyacrylamide gel electrophoresis demonstrated the existence of two phosphorylated intermediates with apparent molecular masses of 60 and 100 kDa. Only phosphorylation of the 100-kDa polypeptide was inhibited by vanadate. The membrane extract containing Na⁺-stimulated ATPase, when reconstituted into soybean phospholipid vesicles, exhibited ²²Na⁺ transport by the addition of ATP, which was inhibited by vanadate and gramicidin. It is likely that the Na⁺-stimulated ATPase belongs to P-type and is involved in Na⁺ transport.