A Na+-translocating ATPase was discovered in a gram-positive bacterium Ente
rococcus hirae. Our biochemical and molecular biological studies revealed t
hat this Na+-ATPase belongs to the vacuolar-type enzyme. Purified Na+-ATPas
e consisted of nine subunits: NtpA, B, C, D, E, F, G, I, and K; reconstitut
ed proteoliposomes showed ATP-driven electrogenic Na+ translocation. All th
ese subunits were encoded by the ntp operon: ntpFIKECGABDHJ. The deduced am
ino acid sequences of the major subunits, A, B, and K (16 kDa proteolipid),
were highly similar to those of A, B, and proteolipid subunits of vacuolar
ATPases, although the similarities of other subunits were moderate. The nt
pJ gene encoded a K+ transporter independent of the Na+-ATPase. Expression
of this operon, encoding two transport systems for Na+ and K+ ions, was reg
ulated at transcriptional level by intracellular Na+ as the signal. Two rel
ated cation pumps, vacuolar Na+-ATPase and F0F1, H+-ATPase, coexist in this
bacterium.