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Journal of Bacteriology, August 1998, p. 3799-3803, Vol. 180, No. 15
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Photosynthetic Electron Transport Involved in PxcA-Dependent Proton Extrusion in Synechocystis sp. Strain PCC6803: Effect of pxcA Inactivation on CO₂, HCO₃, and NO₃ Uptake

Masatoshi Sonoda,¹ Hirokazu Katoh,² Wim Vermaas,³ George Schmetterer,⁴ and Teruo Ogawa^1,2,*

Graduate School of Bioagricultural Sciences¹ and Bioscience Center,² Nagoya University, Nagoya 464-01, Japan; Department of Plant Biology and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, AZ 85287-1601³; and Institute of Physical Chemistry, University of Vienna, A-1090 Vienna, Austria⁴

Received 9 February 1998/Accepted 20 May 1998

The product of pxcA (formerly known as cotA) is involved in light-induced Na⁺-dependent proton extrusion. In the presence of 2,5-dimethyl-p-benzoquinone, net proton extrusion by Synechocystis sp. strain PCC6803 ceased after 1 min of illumination and a postillumination influx of protons was observed, suggesting that the PxcA-dependent, light-dependent proton extrusion equilibrates with a light-independent influx of protons. A photosystem I (PS I) deletion mutant extruded a large number of protons in the light. Thus, PS II-dependent electron transfer and proton translocation are major factors in light-driven proton extrusion, presumably mediated by ATP synthesis. Inhibition of CO₂ fixation by glyceraldehyde in a cytochrome c oxidase (COX) deletion mutant strongly inhibited the proton extrusion. Leakage of PS II-generated electrons to oxygen via COX appears to be required for proton extrusion when CO₂ fixation is inhibited. At pH 8.0, NO₃ uptake activity was very low in the pxcA mutant at low [Na⁺] (~100 µM). At pH 6.5, the pxcA strain did not take up CO₂ or NO₃ at low [Na⁺] and showed very low CO₂ uptake activity even at 15 mM Na⁺. A possible role of PxcA-dependent proton exchange in charge and pH homeostasis during uptake of CO₂, HCO₃, and NO₃ is discussed.

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^* Corresponding author. Mailing address: Bioscience Center, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan. Phone: 81-52-789-5215. Fax: 81-52-789-5214. E-mail: h44975a{at}nucc.cc.nagoya-u.ac.jp.

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Journal of Bacteriology, August 1998, p. 3799-3803, Vol. 180, No. 15
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

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