Kinetics of plastoquinol oxidation by the Q-cycle in leaves
| Autor: | Agu Laisk, Vello Oja, Hillar Eichelmann |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Chlorophyll
0106 biological sciences 0301 basic medicine Light Plastoquinone Kinetics Light-Harvesting Protein Complexes Biophysics Photochemistry Photosynthesis Models Biological 01 natural sciences Biochemistry Q cycle Electron Transport 03 medical and health sciences Plastocyanin Plant Proteins Membrane potential P700 Photosystem I Protein Complex ATP synthase biology Chemistry Cell Biology Electron transport chain Cytochromes f Plant Leaves Cytochrome b6f Complex 030104 developmental biology biology.protein Helianthus Oxidation-Reduction Algorithms 010606 plant biology & botany |
| Zdroj: | Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1857:819-830 |
| ISSN: | 0005-2728 |
| Popis: | Electrochromic shift measurements confirmed that the Q-cycle operated in sunflower leaves. The slow temporarily increasing post-pulse phase was recorded, when ATP synthase was inactivated in the dark and plastoquinol (PQH(2)) oxidation was initiated by a short pulse of far-red light (FRL). During illumination by red light, the Q-cycle-supported proton arrival at the lumen and departure via ATP synthase were simultaneous, precluding extreme build-up of the membrane potential. To investigate the kinetics of the Q-cycle, less than one PQH(2) per cytochrome b(6)f (Cyt b(6)f) were reduced by illuminating the leaf with strong light pulses or single-turnover Xe flashes. The post-pulse rate of oxidation of these PQH2 molecules was recorded via the rate of reduction of plastocyanin (PC(+)) and P700(+), monitored at 810 and 950 nm. The PSII-reduced PQH(2) molecules were oxidized with multi-phase overall kinetics, τ(d)=1, τ(p)=5.6 and τ(s)=16 ms (22 °C). We conclude that τ(d) characterizes PSII processes and diffusion, τ(p) is the bifurcated oxidation of the primary quinol and τ(s) is the Q-cycle-involving reduction of the secondary quinol at the n-site, its transport to the p-site, and bifurcated oxidation there. The extraordinary slow kinetics of the Q-cycle may be related to the still unsolved mechanism of the "photosynthetic control." |
| Databáze: | OpenAIRE |
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