The plasma membrane H+-ATPase, encoded by the PMA1 gene, is the essential and main primary yeast transporter belonging to the widely distributed family of P2-type ATPases (7). In yeast cells, it is the most abundant plasma membrane protein, which is very stable and consumes at least 20% of cellular ATP (177). Its electrogenic activity creates the electrochemical gradient of protons across the plasma membrane, which is in turn indispensable for all secondary active symporters and antiporters. The activity of Pma1 is tightly regulated according to the metabolic activity and physiological conditions of cells; e.g., external glucose is a powerful stimulus leading to a rapid and strong activation (254). Its activity is also positively regulated in response to decreased intracellular pH or increased potassium uptake (258). S. cerevisiae encodes a second plasma membrane H+-ATPase, Pma2, which is 89% identical to Pma1 (252). Pma2 is able to export protons, although its enzymatic properties differ from those of Pma1 (267). The expression of PMA2 under standard growth conditions is much lower than that of PMA1, which explains the nonessential nature of the former and its minor impact on cation homeostasis.