The necessity of PPi and H+-PPiase in maintaining the vacuolar proton gradient in metabolic inhibitor-treated cells.

In Acerpseudoplantanus cells, the effect of metabolic inhibitors (KCN and 2-deoxy-D-glueose) on vacuolar proton gradient, monitored by acridine orange, was assayed. Potassium cyanide plus 2-deoxy-D-glueose slightly lowered this gradient, while strongly decreased cellular ATP level and halved inorganic pyrophosphate (PPi) content. Two inhibitors of phosphatases (imidodiphosphate and KF) restored the PPi level in metabolic inhibitor-treated cells, but decreased the vacuolar proton gradient by inhibiting H§ These results show, henoe, that tonoplast H§ is especially responsible for the maintenance of vacuolar ApH and that this enzyme is the major consumer of cytoplasmic PPi in metabolic inhibitor-treated cells.