C-TERMINAL DELETION ANALYSIS OF PLANT PLASMA-MEMBRANE H-ATPASE - YEAST AS A MODEL SYSTEM FOR SOLUTE TRANSPORT ACROSS THE PLANT PLASMA-MEMBRANE()

The plasma membrane proton pump (H+-ATPase) energizes solute uptake by secondary transporters. Wild-type Arabidopsis plasma membrane H+-ATPa se (AHA2) and truncated H+-ATPases lacking 38, 51, 61, 66, 77, 92, 96, and 104 C-terminal amino acids were produced in yeast. All AHA2 speci es were correctly targeted to the yeast plasma membrane and, in additi on, accumulated in internal membranes. Removal of 38 C-terminal residu es from AHA2 produced a high-affinity state of plant H+-ATPase with a low K-m value (0.1 mM) for ATP. Removal of an additional 12 amino acid s from the C terminus resulted in a significant increase in molecular activity of the enzyme. There was a close correlation between molecula r activity of the various plant H+-ATPase species and their ability to complement mutants of the endogenous yeast plasma membrane H+-ATPase (pma1). This correlation demonstrates that, at least in this heterolog ous host, activation of H+-ATPase is a prerequisite for proper energiz ation of the plasma membrane.