PLANT PHYSIOLOGY , Vol 102, Issue 1 261-267, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Chloroplast Inner-Envelope ATPase Acts as a Primary H+ Pump
G. A. Berkowitz and J. S. Peters
Plant Science Department, Cook College, Rutgers-The State University of New Jersey, New Brunswick, New Jersey 08903
The stromal pH of the chloroplast must be maintained higher than that of
the surrounding cytosol for photosynthetic carbon assimilation to occur.
Experimental evidence demonstrating how this is accomplished in the plant
cell is lacking. In the experiments reported here, we studied H+ and K+
flux across membranes of purified chloroplast inner-envelope vesicles. We
were able to demonstrate ATP-dependent transport of both cations across the
membranes of these vesicles. The data presented document the presence of an
H+-pump ATPase in the chloroplast envelope. Energy-dependent K+ flux across
these membranes occurs as a consequence of primary H+ pumping. The
H+-pumping activity demonstrated in this report is consistent with a model
involving the activity of this envelope ATPase as a primary mechanism
facilitating a stroma:cytosol [delta]pH.
