Universiẗat, Diss., 2004--Osnabrück.

Im Wasser-oxidierenden Cluster („oxygen-evolving complex“, OEC) des Photosystem II findet sich die primäre Quelle der Sauerstoffproduktion der Erde. Der OEC katalysiert in grünen Pflanzen unter Absorption von Sonnenlicht die Vierelektronen-Oxidation von Wasser zu Sauerstoff in einer zyklischen Sequenz von Oxidationszuständen (Kok-Zyklus). In dieser Arbeit wurden Strukturen, Spindichteverteilungen sowie EPR-Parameter ein-, zwei- und vierkerniger Mangankomplexe, die in Bezug auf den OEC modelliert wurden, mit Hilfe der Dichtefunktionaltheorie (DFT) berechnet. Hauptziel war das Verständnis der molekularen und elektronischen Struktur des vierkernigen Manganclusters des OEC durch direkten Vergleich mit experimentellen EPR-Daten. / Photosynthesis is the most fundamental process of life on earth. The biological production of oxygen in plant photosynthesis occurs in photosystem II (PSII). Here two water molecules are coupled in a four-electron oxidation to one O2 molecule, catalyzed by a tetranuclear manganese complex, known as the oxygen-evolving complex (OEC). In this thesis, density-functional theory (DFT) methods were validated and subsequently employed to study structures, spin-density distributions and EPR parameters of mono-, di-, and tetranuclear complexes with regard to the OEC. The goal was to draw conclusions on the molecular and electronic structure of the OEC.

All photosynthetic organisms use light as a source of energy, however prolonged excessively high light causes irreversible damage to the main photosynthetic complexes. In particular the D1 polypeptide of Photosystem II is susceptible to damage and must be degraded and replaced. While the concept of PSII repair has attracted intensive research, important details remain to be determined. The sub-cellular localisation of proteases involved in PSII repair and assembly is investigated here in the model cyanobacterium Synechocystis sp. PCC 6803, by employing fluorescent protein tagging and fluorescence imaging in vivo. Results show that all FtsH protease homologues in Synechocystis are localised to distinct regions of the plasma membrane (FtsH1) and thylakoids (FtsH2, FtsH3, FtsH4). Importantly, FtsH2, involved in PSII repair, remains within distinct thylakoid membrane zones when activated by high light, leading to the hypothesis of localised PSII repair centres in the thylakoid membranes. In order to assess composition of the FtsH2-defined membrane zones, a novel technique for isolating membrane sub-fractions by anti-GFP pulldowns was employed. Mass spectrometry identified potentially interacting and neighbouring proteins within the repair centres, whose content changes under different light exposure. Furthermore, observed changes in FtsH2 and FtsH4 distributions under iron and copper deprivation suggest functions in responses to other stress conditions. To find the locations of D1 synthesis during PSII repair and de novo assembly, the D1 C-terminal processing peptidase CtpA was similarly GFP-tagged and observed in vivo. Results suggest that D1 synthesis for PSII repair takes place in the thylakoid membranes, while D1 synthesis for de novo PSII biogenesis takes place in specialised regions at both edges of the thylakoid system, adjacent to the plasma membrane and protruding into the central cytoplasm. By localising crucial cellular enzymes in vivo, this study demonstrates functional compartmentalisation and membrane heterogeneity in a prokaryote.

Ulm, Univ., Diss., 2008.

Universiẗat, Diss., 2003--München.

Universiẗat, Diss., 2002--Bremen.

Universiẗat, Diss., 2000--Bremen.

Techn. University, Diss., 2003--Berlin.

Techn. University, Diss., 2004--Berlin.

Techn. University Diss., 2005--Berlin.