Photosystem isolation

Unlike the photosynthetic apparatus of photosynthetic bacteria, that of cyanobacteria consits of two photosystems, PS I and II, connected by an electron transport chain. The only chlorophyll present is chlorophyll a, and, therefore, chlorophylls b—d are not of interest in this article. Chlorophyll a is the principal constituent of PS I. Twenty per cent of isolated pigment-protein complexes contain one P700 per 20—30 chlorophyll a molecules the other 80% contain only chlorophyll a20). The physical and chemical properties of chlorophyll a and its role in photosynthesis have recently been described by Meeks77), Mauzerall75), Hoch60), Butler10), and other authors of the Encyclopedia of Plant Physiology NS Vol. 5. 

In order to be able to isolate both PS1 and PS2 from the thermophilic cyanobacterium Thermosynechococcus elongatus by a one-step procedure and in order to immobilize both photosystems on the surface of the support materials (i.e. the electrodes) in an oriented... 

Bricker, T. M, J. Morvant, N. Masri, H. M. Sutton, L. K. Frankel (1998) Isolation of a highly active photosystem n preparation from Synechocystis 6803 using a histidine tagged mutant of CP 47. Biochim. Biophys. Acta, 1409 50-57... 

Mn was first shown to play an important role in photosynthetic 0 evolution by nutritional studies of algae (7). The stoichiometry of Mn in photosystem II was determined by quantitating Mn released from thylakoid membranes by various treatments (8). These experiments established that Mn is specifically required for water oxidation and that four Mn ions per photosystem II are required for optimal rates of 0 evolution (9). More recently, photosystem II preparations with high rates of Oj evolution have been isolated from a variety of sources (for a review see 10). The isolation of an O2-evolving photosystem II has proved to be a major step forward in both the biochemical and spectroscopic characterization of the O2-evolving system. These preparations contain four Mn ions per photosystem II (11), thus confirming that four Mn ions are functionally associated with each O2-evolving center. 

The Mn-Mn distance of 2.7 A determined by EXAFS is diagnostic of a di-/i-oxo-bridged Mn dimer in photosystem II (33,35). However, one could imagine a number of arrangements of the four Mn ions in photosystem II which contain a di-/i-oxo-bridged structure. Moreover, the observation of two different Mn-Mn distances by EXAFS, could only be accounted for by one of the following three arrangements of Mn a Mn trimer plus one isolated (more than 3.3 A away) Mn mononuclear center, two isolated inequivalent Mn dimers, or a Mn tetramer. 

If we return to the possible arrangements of Mn in photosystem II that are consistent with the EXAFS data, one can rule out the possibility that the Mn ions are arranged as two isolated inequivalent Mn dimers because this arrangement cannot account for the Sj -state g - 4.1 EPR signal. This leaves two possible arrangements of the Mn ions a Mn trimer plus a mononuclear Mn center, or a Mn tetramer. Consequently, one should look for an assignment for the 2-state multiline EPR signal from either a mixed-valence Mn trimer or tetramer rather than from a mixed-valence Mn dimer. 

Simidjiev, L, Barzda, V., Mustardy, L., and Garab, G. 1997. Isolation of lamellar aggregates of the light-harvesting chlorophyll a/b protein complex of photosystem II with long-range chiral order and structural flexibility. Anal. Biochem. 250 169-75. 

Nanba, O. and K. Satoh (1987). Isolation of a photosystem II reaction center consisting of D-l and D-2 polypeptides and cytochrome b-559. Proc. Natl. Acad. Sci., 84 109-112. 

Satoh, K. (1996). Introduction to photosystem II reaction center Isolation and biochemical and biophysical characterization. In D.R. Qrt and C.F. Yocum, eds., Oxygenic Photosynthesis. Boston Kluwer, pp. 193-212. 

Oettmeier, W., K. Masson, C. Fedtke, J. Konze, and R.R. Schmidt (1992). Effect of different photosystem II inhibitors on chloroplasts isolated from species either susceptible or resistant toward s-triazine herbicides. Pestic. Biochem. Physiol., 18 357-367. 

In-vitro approach Data are available in abundance concerning metal effects on isolated chloroplasts (for a review, see Clijsters and Van Assche, 1985). All the metals studied were found to be potential inhibitors of photosystem 2 (PS 2) photosystem 1 (PS 1) was reported to be less sensitive. From the in-vitro experiments, at least two potential metal-sensitive sites can be derived in the photosynthetic electron transport chain the water-splitting enzyme at the oxidising side of PS 2, and the NADPH-oxido-reductase (an enzyme with functional SH-groups) at the reducing side of PS 1 (Clijsters and Van Assche, 1985). Moreover, in vitro, non cyclic photophosphorylation was very sensitive to lead (Hampp et al., 1973 b) and mercury (Honeycutt and Korgmann, 1972). Both cyclic and non-cyclic photophosphorylation were proven to be inhibited by excess of copper (Uribe and Stark, 1982) and cadmium (Lucero et al, 1976). 

Due to the anthraquinone moiety, we tested all compounds for photosystem II (PS II) inhibition using both spinach and com thylakoids. By using both monocot and dicot thylakoids, we accounted for any differences in activity. There was no effect on PS II activity for series 2 analogues (-CH3) (data not shown). However, for series 1 analogues (-OH), there was a 50% decrease in PS II activity at 0.1 pM in thylakoids isolated from spinach (Fig. 1.9A). This was similar for thylakoids isolated from corn (Fig. 1.9B). 

Ford, R.C. and Evans, M.C.W. 1983. Isolation of a photosystem 2 preparation from higher plants with highly enriched oxygen evolution activity. FEBS Lett., 160,159-164. 

The exclusive localisation of photosystem I in stroma lamellae was demonstrated directly by immunogold labelling of isolated thylakoids (Vallon et al. 1985, 1986, 1987b). Monoclonal antibodies raised against the barley photosystem I reaction centre (P700 Chla-Pl or CPI) are incubated with thin sections of wild type... 

By reducing the amount of Triton X-100 relative to the chlorophyll concentration in the initial solubilisation of thylakoids, a denser photosystem I preparation was isolated from the sucrose gradient, with... 

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