Catalytic properties of Na(+)-translocating V-ATPase in Enterococcus hirae.
V-ATPases make up a family of proton pumps distributed widely from bacteria to higher organisms. We found a variant of this family, a Na(+)-translocating ATPase, in a Gram-positive bacterium, Enterococcus hirae. The Na(+)-ATPase was encoded by nine ntp genes from F to D in an ntp operon (ntpFIKECGABDHJ): the ntpJ gene encoded a K(+) transporter independent of the Na(+)-ATPase. Expression of this operon, encoding two transport systems for Na(+) and K(+) ions, was regulated at the transcriptional level by intracellular Na(+) as the signal. Structural aspects and catalytic properties of purified Na(+)-ATPase closely resembled those of other V-type H(+)-ATPases. Interestingly, the E. hirae enzyme showed a very high affinity for Na(+) at catalytic reaction. This property enabled the measurement of ion binding to this ATPase for the first time in the study of V- and F-ATPases. Properties of Na(+) binding to V-ATPase were consistent with the model that V-ATPase proteolipids form a rotor ring consisting of hexamers, each having one cation binding site. We propose here a structure model of Na(+) binding sites of the enzyme.
Department of Biological Science and Technology, Science University of Tokyo, Yamazaki, Chiba, Japan.
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Murata
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Kawano
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Igarashi
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Yamato
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Kakinuma
D000251:Adenosine Triphosphatases / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D002384:Catalysis; D027682:Cation Transport Proteins; D002414:Cations, Monovalent; D016983:Enterococcus / Q000201:enzymology* / Q000235:genetics; D009876:Operon; D011510:Proteolipids / Q000378:metabolism; D017494:Proton Pumps / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases
D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D002414:Cations, Monovalent; D011510:Proteolipids; D017494:Proton Pumps; D012964:Sodium; D000251:Adenosine Triphosphatases; D025262:Vacuolar Proton-Translocating ATPases; C021838:sodium-translocating ATPase; D006180:Proton-Translocating ATPases