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  • 1
    Electronic Resource
    Electronic Resource
    Nuclear mutants of Chlamydomonas reinhardtii defective in the biogenesis of the cytochrome b6f complex (1995)
    Springer
    Plant molecular biology 29 (1995), S. 921-932 
    Details
    ISSN: 1573-5028
    Keywords: Chlamydomonas reinhardtii ; chloroplast gene expression ; insertional mutagenesis ; cytochrome b6f complex ; nuclear-encoded factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The random integration of transforming DNA into the nuclear genome of Chlamydomonas has been employed as an insertional mutagen to generate a collection of photosynthetic mutants that display abnormal steady-state fluorescence levels and an acetate-requiring phenotype. Electron paramagnetic resonance spectroscopy was then used to identify those mutants that specifically lack a functional cytochrome b6f complex. Our analysis of RNA and protein synthesis in five of these mutants reveals four separate phenotypes. One mutant fails to accumulate transcript for cytochrome f, whilst a second displays a severely reduced accumulation of the cytochrome b6 transcript. Two other mutants appear to be affected in the insertion of the haem co-factor into cytochrome b6. The fifth mutant displays no detectable defect in the synthesis of any of the known subunits of the complex. Genetic analysis of the mutants demonstrates that in three cases, the mutant phenotype co-segregates with the introduced DNA. For the mutant affected in the accumulation of the cytochrome f transcript, we have used the introduced DNA as a tag to isolate the wild-type version of the affected gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014966
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  • 2
    Electronic Resource
    Electronic Resource
    A three-dimensional model of the Photosystem II reaction centre of Pisum sativum (1992)
    Springer
    Photosynthesis research 34 (1992), S. 287-300 
    Details
    ISSN: 1573-5079
    Keywords: computer model ; D1 protein ; D2 protein ; manganese cluster binding site
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A three-dimensional model of the core proteins D1 and D2, including the cofactors, that form the Photosystem II reaction centre of pea (Pisum sativum), has been generated. This model was built with a rule-based computer modelling system using the information from the crystal structures of the photosynthetic reaction centres of Rhodopseudomonas viridis and Rhodobacter sphaeroides. An alignment of the primary sequences of twenty three D1, nine D2, eight bacterial L and eight bacterial M subunits predicts strong similarity between bacterial and higher plant reaction centres, especially in the transmembrane region where the cofactors responsible for electron transport are located. The sequence to be modelled was aligned to the bacterial structures using environment-dependent substitution tables to construct matrices, improving the alignment procedure. The ancestral relationship between the bacteria and higher plant sequences allowed both the L and M subunits to be used as structural templates as they were equally related to the higher plant polypeptides. The regions with the highest predicted structural homology were used as a framework for the construction of the structurally conserved regions. The structurally conserved region of the model shows strong similarity to the bacterial reaction centre in the transmembrane helices. The stromal and lumenal loops show greater sequence variation and are therefore predicted to be the structurally variable regions in the model. The key sidechain assignments and residues that may interact with cofactors are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00033446
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopic studies of the manganese complex of Photosystem II (1993)
    Springer
    Photosynthesis research 38 (1993), S. 341-346 
    Details
    ISSN: 1573-5079
    Keywords: oxygen evolving complex (OEC) ; EPR ; EXAFS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Our recent EPR and EXAFS experiments investigating the structure of the oxygen-evolving complex of PS II are discussed. PS II treatments which affect the cofactors calcium and chloride have been used to poise samples in modified forms of the S-states, S1, S2 and S3. X-ray absorption studies indicate a similar overall structure for the manganese complex between treated and native samples although the influence of the treatments and cofactors is observed. Manganese oxidation (or oxidation of a ligand to the manganese cluster) is indicated to occur on each of the transitions S1 →S2 and S2 →S3 in these modified samples. The cluster appears to contain at least two inequivalent Mn-Mn pairs. In the native samples the Mn-Mn distance is 2.7 Å, but in samples where the calcium site is affected, one of the pairs has a 3.0 Å Mn-Mn distance. The intensity of the 3.3/3.6 Å interaction is reduced on sodium chloride treatment (calcium depletion) perhaps indicating calcium binding close to the manganese cluster. From EPR data we also propose that treatments which affect calcium and chloride binding cause a modification of the native S2 state, slow the reduction of Yz • and allow an S3 EPR signal to be observed following illumination. The origin of the S3 EPR signal, a modified S3 or S2 X• where X• is an organic radical of unknown charge, is discussed in relation to the results from the EXAFS studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046759
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  • 4
    Electronic Resource
    Electronic Resource
    Comparative EPR and thermoluminescence study of anoxic photoinhibition in Photosystem II particles (1995)
    Springer
    Photosynthesis research 46 (1995), S. 213-218 
    Details
    ISSN: 1573-5079
    Keywords: Photoinhibition ; Photosystem II ; quinone-iron complex ; electron paramagnetic resonance (EPR) ; thermoluminescence (TL)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosystem II particles were exposed to 800 W m−2 white light at 20 °C under anoxic conditions. The Fo level of fluorescence was considerably enhanced indicating formation of stable-reduced forms of the primary quinone electron acceptor, QA. The Fm level of fluorescence declined only a little. The g=1.9 and g=1.82 EPR forms characteristic of the bicarbonate-bound and bicarbonate-depleted semiquinone-iron complex, QA −Fe2+, respectively, exhibited differential sensitivity against photoinhibition. The large g=1.9 signal was rapidly diminished but the small g=1.82 signal decreased more slowly. The S2-state multiline signal, the oxygen evolution and photooxidation of the high potential form of cytochrome b-559 were inhibited approximately with the same kinetics as the g=1.9 signal. The low potential form of oxidized cytochrome b-559 and Signal IIslow arising from TyrD + decreased considerably slower than the g=1.9 semiquinone-iron signal. The high potential form of oxidized cytochrome b-559 was diminished faster than the low potential form. Photoinhibition of the g=1.9 and g=1.82 forms of QA was accompanied with the appearance and gradual saturation of the spin-polarized triplet signal of P 680. The amplitude of the radical signal from photoreducible pheophytin remained constant during the 3 hour illumination period. In the thermoluminescence glow curves of particles the Q band (S2QA − charge recombination) was almost completely abolished. To the contrary, the C band (TyrD +QA − charge recombination) increased a little upon illumination. The EPR and thermoluminescence observations suggest that the Photosystem II reaction centers can be classified into two groups with different susceptibility against photoinhibition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020433
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    Paper (German National Licenses)
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