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Chloroplast Inner-Envelope ATPase Acts as a Primary H+ Pump
G. A. Berkowitz1, J. S. Peters
1Plant Science Department, Cook College, Rutgers-The State University of New Jersey, New Brunswick, New Jersey 08903.
Plant Physiology
|May 1, 1993
Summary
Plant chloroplasts maintain a higher stromal pH for carbon assimilation using an ATP-dependent proton pump in the inner envelope. This H+-pump ATPase facilitates cation flux, establishing the necessary pH gradient between the stroma and cytosol.
Area of Science:
- Plant biology
- Cellular physiology
- Biochemistry
Background:
- Photosynthetic carbon assimilation requires a higher stromal pH within chloroplasts compared to the cytosol.
- The precise mechanism for establishing and maintaining this pH gradient in plant cells remains unclear.
Purpose of the Study:
- To investigate the transport mechanisms of protons (H+) and potassium ions (K+) across the chloroplast inner envelope.
- To identify the molecular basis for the pH difference between the chloroplast stroma and cytosol.
Main Methods:
- Studied cation flux across purified chloroplast inner-envelope vesicles.
- Utilized assays to demonstrate ATP-dependent transport of H+ and K+.
Main Results:
- Demonstrated ATP-dependent transport of both H+ and K+ across the chloroplast inner-envelope membranes.
- Provided evidence for an H+-pump ATPase located in the chloroplast envelope.
- Showed that energy-dependent K+ flux is a consequence of primary H+ pumping.
Conclusions:
- The chloroplast envelope possesses an H+-pump ATPase activity.
- This ATPase activity is the primary mechanism responsible for establishing the stromal:cytosol pH difference ([delta]pH).
- The findings elucidate a key process in regulating photosynthetic efficiency.