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Journal Article

Chloroplast Inner-Envelope ATPase Acts as a Primary H⁺ Pump

Gerald A. Berkowitz and Jeanne S. Peters
Plant Physiology
Vol. 102, No. 1 (May, 1993), pp. 261-267
Stable URL: http://www.jstor.org/stable/4275170
Page Count: 7

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Topics: Chloroplasts, Adenosine triphosphatases, Cell membranes, Pumps, Plants, pH, P branes, Enzymes, Pumping, Thylakoids
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Chloroplast Inner-Envelope ATPase Acts as a Primary H⁺ Pump
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Abstract

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 ΔpH.

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