| 1. |
- Park, Y I, et al.
(author)
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Role of a novel photosystem II-associated carbonic anhydrase in photosynthetic carbon assimilation in Chlamydomonas reinhardtii
- 1999
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In: FEBS Letters. - 0014-5793 .- 1873-3468. ; 444:1, s. 102-105
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Journal article (peer-reviewed)abstract
- Intracellular carbonic anhydrases (CA) in aquatic photosynthetic organisms are involved in the CO2-concentrating mechanism (CCM), which helps to overcome CO2 limitation in the environment. In the green alga Chlamydomonas reinhardtii, this CCM is initiated and maintained by the pH gradient created across the chloroplast thylakoid membranes by photosystem (PS) II-mediated electron transport. We show here that photosynthesis is stimulated by a novel, intracellular alpha-CA bound to the chloroplast thylakoids. It is associated with PSII on the lumenal side of the thylakoid membranes. We demonstrate that PSII in association with this lumenal CA operates to provide an ample flux of CO2 for carboxylation. (C) 1999 Federation of European Biochemical Societies.
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| 2. |
- Rojdestvenski, I, et al.
(author)
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A carbonic anhydrase catalyzed CO2 pump in Chlamydomonas reinhardtii : In vivo experiments, computer modelling, and theory
- 2000
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In: Russian journal of plant physiology. - 1021-4437 .- 1608-3407. ; 47:5, s. 613-621
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Journal article (peer-reviewed)abstract
- We studied the bicarbonate depletion effects on photosynthesis in high-CO2 grown-cell wall-less mutants of Chlamydomonas reinhardtii with (cw92) and without (cia3/cw15) active carbonic anhydrase (CA) associated with photosystem II (PSII). The mutants were grown in a high-CO2 medium and then washed with a CO2-free buffer. We discuss the shutdown of oxygen evolution in cw92 as a consequence of CO2 depletion of the Calvin cycle. It is suggested that CA acts as part of a PSII-driven pump delivering CO2 from the lumen into the stroma, where it becomes available to the Calvin cycle. Our model is supported by computer simulation data and accommodates the results of in vivo experiments as well as the differences between cw92 and cia3 mutants. We also present a simple theory of the phenomena discussed, based on a time-scale hierarchy approach, which describes the CO2 depletion in cw92 using only two rate constants-V-max and K-m of the Calvin cycle.
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| 3. |
- Rojdestvenski, I, et al.
(author)
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Robustness and time-scale hierarchy in biological systems
- 1999
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In: Biosystems (Amsterdam. Print). - 0303-2647 .- 1872-8324. ; 50:1, s. 71-82
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Journal article (peer-reviewed)abstract
- This study addresses the issue of robustness of biological systems with respect to microscopic parameters, especially the emergence of robustness as a consequence of lime-scale hierarchy, applying naive thermodynamic and dynamic assumptions. Theoretical considerations of how the time-scale hierarchy can decouple physiological regulatory mechanisms are illustrated by two model systems involving the photosynthetic apparatus of green plants. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.
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| 4. |
- Borodich, A, et al.
(author)
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Segregation of the photosystems in higher plant thylakoids and short- and long-term regulation by a mesoscopic approach
- 2003
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In: Journal of Theoretical Biology. - 0022-5193 .- 1095-8541. ; 225:4, s. 431-441
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Journal article (peer-reviewed)abstract
- In this paper we consider the relationship between the lateral segregation of photosystems I and II in the grana and characteristics of the short- and long-term regulation in thylakoids following the mesoscopic approach. Our study is thermodynamic; it is based on the Flory-Huggins theory for binary mixtures and the McMillan-Mayer theory of heterogeneous solutions. We demonstrate that state transitions promote rearrangement of photosystems by either favoring their mixing after LHCII phosphorylation or enhancing their segregation after LHCII dephosphorylation. This regulation influences the entire system properties locally. We also demonstrate that the variations of the photosystem ratio promote rearrangement of the photosystems preserving their segregation. This regulation influences the entire system properties globally. The studies presented are another indication of the importance of the segregation of the photosystems in the grana thylakoids of higher plants. Segregation of PSIs and PSIIs is a signature of the spinodal decomposition, which is a fine regulatory mechanism, related to both the short- and long-term adaptations of the photosynthetic apparatus in higher plant thylakoids. (C) 2003 Elsevier Ltd. All rights reserved.
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| 5. |
- Borodich, A, et al.
(author)
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Segregation of the photosystems in thylakoids depends on their size
- 2003
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In: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1606:1-3, s. 73-82
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Journal article (peer-reviewed)abstract
- Lateral segregation of two types of photosystems in thylakoid membranes of green plants is one of the key factors that provide the stability and fine-tuning of the light quanta supply by pigment proteins and non-cyclic electron transport. Due to this specific feature of the membrane structural organization, the photosynthetic units function in the green plants with optimal performance. In this report a mesoscopic theory is outlined to address the physical aspects of segregation phenomenon. Results of theoretical studies and computer simulations suggest that charge mismatch and the size difference between two photosystems in grana are most responsible for their lateral segregation, which is driven by the screened electrostatic and lipid-induced interactions. Comparative simulations of photosystems of different sizes show the crucial dependence of their ordering on a geometrical parameter. It seems that the size effect alone may prevent photosystems from segregated arrangement in cyanobacterial thylakoids. (C) 2003 Elsevier B.V. All rights reserved.
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| 6. |
- Rojdestvenski, I, et al.
(author)
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A two-dimensional many-body system with competing interactions as a model for segregation of photosystems in thylakoids of green plants
- 2000
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In: European Biophysics Journal. - 0175-7571 .- 1432-1017. ; 29:3, s. 214-220
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Journal article (peer-reviewed)abstract
- We address the segregation of photosystems I (PSI) and II (PSII) in thylakoid membranes by means of a molecular dynamics method. We assume a two-dimensional (in-plane) problem with PSI and PSII being represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and am exponentially decaying attractive part. Our modeling results suggest that the system may have a complicated phase behavior, including a quasi-crystalline phase at low ionic screenmg, a disordered phase and: in addition, a possible "clotting" agglomerate phase at high screening where the photosystems tend to clot together. The relevance of the observed phenomena to the stacking of thylakoid membranes is discussed.
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| 7. |
- Rojdestvenski, I, et al.
(author)
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Segregation of photosystems in thylakoid membranes as a critical phenomenon
- 2002
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In: Biophysical Journal. - 0006-3495 .- 1542-0086. ; 82:4, s. 1719-1730
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Journal article (peer-reviewed)abstract
- The distribution of the two photosystems, PSI and PSII, in grana and stroma lamellae of the chloroplast membranes is not uniform. PSII are mainly concentrated in grana and PSI in stroma thylakoids. The dynamics and factors controlling the spatial segregation of PSI and PSII are generally not well understood, and here we address the segregation of photosystems in thylakoid membranes by means of a molecular dynamics method. The lateral segregation of photosystems was studied assuming a model comprising a two-dimensional (in-plane), two-component, many-body system with periodic boundary conditions and competing interactions between the photosystems in the thylakoid membrane. PSI and PSII are represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and an exponentially decaying attractive part. The modeling results suggest a complicated phase behavior of the system, including quasi-crystalline phase of randomly distributed complexes of PSII and PSI at low ionic screening, well defined clustered state of segregated complexes at high screening, and in addition, an intermediate agglomerate phase where the photosystems tend to aggregate together without segregation. The calculations demonstrated that the ordering of photosystems within the membrane was the result of interplay between electrostatic and lipid-mediated interactions. At some values of the model parameters the segregation can be represented visually as well as by analyzing the correlation functions of the configuration.
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| 8. |
- Rojdestvenski, I, et al.
(author)
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Thermodynamics of complexity
- 2003
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In: Physica A. - 0378-4371 .- 1873-2119. ; 320, s. 318-328
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Journal article (peer-reviewed)abstract
- The definition of complexity, simultaneously introduced by Kolmogorov and Chaitin, has given a numerical measure to what was previously defined only at an intuitive level. This measure, useful as it is, becomes hard to utilise when one deals with the complexity of most real systems, and biological objects in particular. We try to overcome this difficulty by discussing a possible thermodynamic definition of complexity based on energy balance. The Kolmogorov-Chaitin definition of complexity thus relates to our thermodynamic definition in a similar way as the probabilistic definition of entropy relates to the thermodynamic one. In the framework of this intuitive treatment it is discussed how the complexity of a biological system may depend on the variability of the environmental conditions. A specific illustration of this approach is given using some numerical modeling examples. (C) 2002 Elsevier Science B.V. All rights reserved.
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