Limiting steps in photosystem II and water decomposition in Chlorella and spinach chloroplasts
| Autor: | B. Bouges-Bocquet |
|---|---|
| Rok vydání: | 1973 |
| Předmět: |
Chloroplasts
Time Factors Photosystem II Light Macromolecular Substances First-order reaction Kinetics Biophysics Chlorella Biochemistry Redox Models Biological chemistry.chemical_compound Hydroxylamine Chlorophyta Plant Cells Photosynthesis chemistry.chemical_classification Water Cell Biology Rate equation Electron acceptor Darkness Plants Decomposition Oxygen Crystallography chemistry Physical chemistry Mathematics Polarography |
| Zdroj: | Biochimica et biophysica acta. 292(3) |
| ISSN: | 0006-3002 |
| Popis: | 1. 1. By varying the redox potential of a chloroplast suspension, we obtained new evidence for an equilibrium between states S 0 and S 1 in the model of Kok, B., Forbush, B. and McGloin, N. (1970, Photochem. Photobiol. 11, 457–475). The mid-point potential of the S 0 to S 1 couple is close to that for the pool of the electron acceptor of System II, A to A − . 2. 2. The limiting steps between two consecutive photoreactions of System II in Chlorella and spinach chloroplasts, have been studied. 2.1. (a) The limiting step from S 1 to S 2 (noted γ 1 ( Δt )) is not exponential. Its temperature coefficient becomes greater as the reaction proceeds. The shape of the kinetics is an intrinsic property of each center. Chloroplasts fixed with 2% glutaraldehyde, show simple first order kinetics. 2.2. (b) The limiting step from S 0 to S 1 ( γ 0 ( Δt )) exhibits the same characteristics as γ 1 ( Δt )). 2.3. (c) The limiting step from S 2 to S 3 ( γ 2 ( Δt )) shows sigmoidal kinetics; two reactions are involved. One of the reactions exhibits the same properties as γ 0 ( Δt ) and γ 1 ( Δt ). 2.4. (d) The limiting step from S 3 to S 0 ( γ 3 ( Δt )) is a first order reaction, two times slower than the other transitions. This reaction is interpretated in terms of oxygen release. 3. 3. We also studied the limiting steps in the presence of low concentrations (50 μM) of hydroxylamine. The results favor the binding of two molecules of hydroxylamine to every photochemical center. |
| Databáze: | OpenAIRE |
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