A PHOSPHOTHREONINE RESIDUE AT THE C-TERMINAL END OF THE PLASMA-MEMBRANE H-ATPASE IS PROTECTED BY FUSICOCCIN-INDUCED 14-3-3 BINDING()

We have isolated the plasma membrane H+-ATPase in a phosphorylated for m from spinach (Spinacia oleracea L.) lear tissue incubated with fusic occin, a fungal toxin that induces irreversible binding of 14-3-3 prot ein to the C terminus of the H+-ATPase, thus activating H+ pumping. We have identified threonine-948, the second residue from the C-terminal end of the H+-ATPase, as the phosphorylated amino acid. Turnover of t he phosphate group of phosphothreonine-948 was inhibited by 14-3-3 bin ding, suggesting that this residue may form part of a binding motif fo r 14-3-3. This is the first identification to our knowledge of an in v ivo phosphorylation site in the plant plasma membrane H+-ATPase.