Regulation and Reversibility of Vacuolar H+-ATPase
T. Hirata, N. Nakamura, H. Omote, Y. Wada, and M. Futai
Fungal and yeast vacuoles possess the V-ATPase as the sole proton pump,
whereas those of higher plants contain V-ATPase and a proton translocating
pyrophosphatase (V-PPase). Arabidopsis thaliana vacuolar H+-translocating
pyrophosphatase (V-PPase) can be expressed in yeast as a functional vacuolar
proton pump with endogenous vacuolar H+-ATPase (V-ATPase), and
the regulation and reversibility of electrochemical proton gradient (DpH).
In this study, we demonstrated that V-ATPase can synthesize ATP coupled
with DmH generated by V-PPase and that proton
translocation by the two pumps is not strictly regulated by DpH.
In addition, the ATP synthesis was sensitive to bafilomycin A1 which gives
two Km values for ADP and it was not observed in the addition of nigericin
which dissipates DpH not DY,
indicating that V-ATPase is a reversible enzyme and DpH
is essential for ATP synthesis.
1. Electrogenic H+-Pumping Pyrophosphatase in Tonoplast Vesicles of Oat
Root. Wang, Y., Leigh, R. A., Kaestner, K. L., and Sze, H., Plant
Physiol. 81, 497-502, 1986.
2. Chemiosmotic Coupling if Ion Transport in the Yeast Vacuole: Its
Role in Acidification Inside Organelles. Wada, Y., and Anraku, Y.,
Bioenerg. Biomembr. 26, 631-637, 1994.
3. Reversibility of H+-ATPase and H+-Pyrophosphatase
in Tonoplast Vesicles from Maize Coleptiles and Seeds. Rocha Facanha, A.,
de Meis, L. Plant Physiol. 116, 1487-1495, 1998.