Glucose addition to budding yeast causes a short-term decrease of
intracellular pH because of glucose metabolism. The pH is restored to
its normal value by the vacuolar accumulation of protons by the vacuolar
V-ATPase [7] and proton release to the extracellular medium by
plasma membrane H+-ATPase (Pma1p). It has been proposed that
the pH decrease is necessary for Pma1p activation because plasma
membrane-permeable organic acids activate Pma1p even in the absence
of glucose [2]