Photosynthetic electron transport involved in PxcA-dependent proton extrusion in Synechocystis sp. Strain PCC6803: effect of pxcA inactivation on CO2, HCO3-, and NO3- uptake.
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+] (approximately 100 microM). 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.
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-01, Japan.
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M
Sonoda
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H
Katoh
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W
Vermaas
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G
Schmetterer
T
T
Ogawa
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002245:Carbon Dioxide / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000235:genetics; D017353:Gene Deletion; D005985:Glyceraldehyde / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins; D009154:Mutation; D009566:Nitrates / Q000378:metabolism*; D010788:Photosynthesis; D011522:Protons
D001426:Bacterial Proteins; D001639:Bicarbonates; D008565:Membrane Proteins; D009566:Nitrates; D011522:Protons; C099434:pcxA protein, Synechocystis; D002245:Carbon Dioxide; D005985:Glyceraldehyde; D003576:Electron Transport Complex IV