A Vacuolar-Type H+-ATPase in a Nonvacuolar Organelle Is Required for the Sorting of Soluble Vacuolar Protein Precursors in Tobacco Cells.

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In plant cells, vacuolar matrix proteins are separated from the secretory proteins at the Golgi complex for transport to the vacuoles. To investigate the involvement of vacuolar-type ATPase (V-ATPase) in the vacuolar targeting of soluble proteins, we analyzed the effects of bafilomycin A1 and concanamycin A on the transport of vacuolar protein precursors in tobacco cells. Low concentrations of these inhibitors caused the missorting of several vacuolar protein precursors; sorting was more sensitive to concanamycin A than to bafilomycin A1. Secretion of soluble proteins from tobacco cells was also inhibited by bafilomycin A1 and concanamycin A. We next analyzed the subcellular localization of V-ATPase. V-ATPase was found in a wide variety of endomembrane organelles. Both ATPase activity and ATP-dependent proton-pumping activity in the Golgi-enriched fraction were more sensitive to concanamycin A than to bafilomycin A1, whereas these activities in the tonoplast fraction were almost equally sensitive to both reagents. Our observations indicate that the V-ATPase in the organelle that was recovered in the Golgi-enriched fraction is required for the transport of vacuolar protein precursors and that this V-ATPase is distinguishable from the tonoplast-associated V-ATPase.

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