Dokument: Ultrafast optical spectroscopy of the electron transfer and protein dynamics in Photosystem II
| Titel: | Ultrafast optical spectroscopy of the electron transfer and protein dynamics in Photosystem II | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=10779 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20090326-095945-7 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Szczepaniak, Malwina [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Holzwarth, Alfred R. [Gutachter] Prof. Dr. Pretzler, Georg [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 530 Physik | |||||||
| Beschreibung: | Oxygenic photosynthesis is regarded as one of the most important biological processes given that it provides the molecular oxygen, without which life of many organisms would not be possible. Photosynthesis is an interesting and also challenging issue per se, due to its complexity and the highly evolved diverse contributing processes. Nevertheless, in the present day probably the most crucial reason for a detailed study of the photosynthetic reactions lies in the search of alternative sources of energy. Photosynthetic organisms know how to use solar energy, and the knowledge how they capture light, as well as store and utilize the absorbed energy is essential for the development of artificial systems that mimic the work of plants and algae. For this reason it is necessary to understand the primary processes taking place in the photosynthetic reaction center – the energy transfer properties, pathways, bottlenecks and limitations, as well as the details of the electron transfer processes. Moreover, one should keep in mind that all of the mentioned reactions are perfectly regulated by the surrounding medium, namely protein matrix, to achieve highest efficiencies and least losses.
In the current work the validity of the ERPE model (“exciton/radical pair equilibrium model”) was tested in several time-resolved picosecond fluorescence experiments on intact Photosystem II (PSII) core complexes. Data analysis of the kinetics of PSII with open reaction centers (RCs) allowed resolving the very fast (~ 1.5 ps) energy transfer process from the antenna complexes, CP43 and CP47, to the RC, and the slower (7 ps) charge separation (CS) step. Compartmental modeling let us for the first time resolve the fluorescence spectrum of the excited RC and determine the two early radical pairs (RPs) formed prior to the reduction of quinone QA. Analysis of the data demonstrates that the kinetics in PSII is definitely trap-limited. The experiment on PSII with open RCs performed with the synchroscan streak camera (SC) system confirms the presence of lifetimes found in the earlier study. Moreover, the higher time-resolution allowed determination of additional component in a subpicosecond range (0.95 ps) that possibly can be assigned to an even faster energy transfer in the antenna complexes. An important outcome of the present study concerns the protein dynamics observed in PSII. Such protein relaxation steps were resolved in the PSII particles with both, open and closed RCs. We show that the protein senses the formed RPs and subsequently undergoes relaxation to an energetically more favorable state. Additionally, our studies on the PSII lacking tyrosine D (TyrD) show that the enzyme can maintain its “normal” efficiency in the absence of this amino acid residue. However, the lack of TyrD is clearly visible in the second electron transfer step in PSII with oxidized QA. Nevertheless, the surrounding protein balances the lack of TyrD, which is demonstrated in the comparable total losses of free energy in both, WT’ (WT with attached His-tag on CP43) and TyrD-lacking PSII. The studies on the TyrD-lacking PSII support our hypothesis that in PSII with closed RCs pheophytin is not reduced and that the CS and the electron transfer mechanism is altered upon the closure of the RCs. The comparison of the free energy levels of WT’ and D2-Y160F mutant PSII suggests that the cofactors on the D2 side of the RC may be involved in electron transfer. It implies activation of the D2 branch when the RCs are closed in the high light conditions. This idea was further investigated with the nanosecond transient absorption spectroscopy. The results show the triplet β-carotene (Car) signal formed on the time scale of about 190 ns, which was assigned to the Car on the D2 branch of the RC. Thus, we propose a photoprotective function for D2 side of the RC. In the suggested mechanism the triplet chlorophyll (3Chl) is formed by a radical pair mechanism on the D2 branch, and subsequently is quenched by the CarD2. To conclude, present work shows the bottleneck in the energy trapping processes, as well as the importance of the protein surrounding for the efficient performance of the enzyme. Moreover, a new protection mechanism activated in the high light conditions is proposed. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Physik | |||||||
| Dokument erstellt am: | 27.03.2009 | |||||||
| Dateien geändert am: | 25.03.2009 | |||||||
| Promotionsantrag am: | 17.12.2008 | |||||||
| Datum der Promotion: | 28.01.2009 |
