Activation of the plasma membrane H (+) -ATPase by acid stress: antibodies as a tool to follow the phosphorylation status of the penultimate activating Thr.

Tight regulation of the plasma membrane proton pump ATPase (H (+) -ATPase) is necessary for controlling the membrane potential that energizes secondary transporters. This regulation relies on the phosphorylation of the H (+) -ATPase penultimate residue, a theonine, and the subsequent binding of regulatory 14-3-3 proteins, which results in enzyme activation. Using phospho-specific antibodies directed against the phosphorylable Thr of either PMA2 (Plasma membrane H (+) -ATPase from N. plumbaginifolia) or PMA4, we showed that the kinetics and extent of phosphorylation differ between both isoforms according to the growth or environmental conditions like cold stress. (1) Here, we used phospho-specific antibodies to follow PMA2 Thr phosphorylation upon acidification of the cytosol by incubating N. tabacum BY2 cells with four different weak organic acids. Increased PMA2 phosphorylation was observed for three of them, thus highlighting the role of the H (+) -ATPase in cell pH homeostasis.