CHLOROPLAST INNER-ENVELOPE ATPASE ACTS AS A PRIMARY H+ PUMP

The stromal pH of the chloroplast must be maintained higher than that of the surrounding cytosol for photosynthetic carbon assimilation to o ccur. Experimental evidence demonstrating how this is accomplished in the plant cell is lacking. In the experiments reported here, we studie d H+ and K+ flux across membranes of purified chloroplast inner-envelo pe vesicles. We were able to demonstrate ATP-dependent transport of bo th 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 conseque nce of primary H+ pumping. The H+-pumping activity demonstrated in thi s report is consistent with a model involving the activity of this env elope ATPase as a primary mechanism facilitating a stroma:cytosol DELT ApH.