Journal of Biological Chemistry
Volume 286, Issue 32, 12 August 2011, Pages 28089-28096
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Cell Biology
Consequences of Loss of Vph1 Protein-containing Vacuolar ATPases (V-ATPases) for Overall Cellular pH Homeostasis*

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In yeast cells, subunit a of the vacuolar proton pump (V-ATPase) is encoded by two organelle-specific isoforms, VPH1 and STV1. V-ATPases containing Vph1 and Stv1 localize predominantly to the vacuole and the Golgi apparatus/endosomes, respectively. Ratiometric measurements of vacuolar pH confirm that loss of STV1 has little effect on vacuolar pH. Loss of VPH1 results in vacuolar alkalinization that is even more rapid and pronounced than in vma mutants, which lack all V-ATPase activity. Cytosolic pH responses to glucose addition in the vph1Δ mutant are similar to those in vma mutants. The extended cytosolic acidification in these mutants arises from reduced activity of the plasma membrane proton pump, Pma1p. Pma1p is mislocalized in vma mutants but remains at the plasma membrane in both vph1Δ and stv1Δ mutants, suggesting multiple mechanisms for limiting Pma1 activity when organelle acidification is compromised. pH measurements in early prevacuolar compartments via a pHluorin fusion to the Golgi protein Gef1 demonstrate that pH responses of these compartments parallel cytosolic pH changes. Surprisingly, these compartments remain acidic even in the absence of V-ATPase function, possibly as a result of cytosolic acidification. These results emphasize that loss of a single subunit isoform may have effects far beyond the organelle where it resides.

Organellar pH Homeostasis
Proton Pumps
Vacuolar Acidification
Vacuolar ATPase
Yeast

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*

This work was supported, in whole or in part, by National Institutes of Health Grant R01 GM50322 (to P. M. K.).

1

Present address: Facultad de Medicina, Universidad Juárez del Estado de Durango(UJED), Gómez Palacio, Durango, México.