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  • 1
    Electronic Resource
    Electronic Resource
    ENDOR and Special TRIPLE Resonance Spectroscopy of QA.bul.- of Photosystem 2 (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 12075-12081 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00037a051
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  • 2
    Electronic Resource
    Electronic Resource
    The role of trace metals in photosynthetic electron transport in O2-evolving organisms (1999)
    Springer
    Photosynthesis research 60 (1999), S. 111-150 
    Details
    ISSN: 1573-5079
    Keywords: calcium ; copper ; iron ; manganese ; oxygen evolution ; phylogeny ; zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Iron is the quantitatively most important trace metal involved in thylakoid reactions of all oxygenic organisms since linear (= non-cyclic) electron flow from H2O to NADP+ involves PS II (2–3 Fe), cytochrome b6-f (5 Fe), PS I (12 Fe), and ferredoxin (2 Fe); (replaceable by metal-free flavodoxin in certain cyanobacteria and algae under iron deficiency). Cytochrome c6 (1 Fe) is the only redox catalyst linking the cytochrome b6-f complex to PS I in most algae; in many cyanobacteria and Chlorophyta cytochrome c6 and the copper-containing plastocyanin are alternatives, with the availability of iron and copper regulating their relative expression, while higher plants only have plastocyanin. Iron, copper and zinc occur in enzymes that remove active oxygen species and that are in part bound to the thylakoid membrane. These enzymes are ascorbate peroxidase (Fe) and iron-(cyanobacteria, and most al gae) and copper-zinc- (some algae; higher plants) superoxide dismutase. Iron-containing NAD(P)H-PQ oxidoreductase in thylakoids of cyanobacteria and many eukaryotes may be involved in cyclic electron transport around PS I and in chlororespiration. Manganese is second to iron in its quantitative role in the thylakoids, with four Mn (and 1 Ca) per PS II involved in O2 evolution. The roles of the transition metals in redox catalysts can in broad terms be related to their redox chemistry and to their availability to organisms at the time when the pathways evolved. The quantitative roles of these trace metals varies genotypically (e.g. the greater need for iron in thylakoid reactions of cyanobacteria and rhodophytes than in other O2-evolvers as a result of their lower PS II:PS I ratio) and phenotypically (e.g. as a result of variations in PS II:PS I ratio with the spectral quality of incident radiation).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006282714942
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of the proposed Fe-SX binding region of Photosystem 1 by site directed mutation of PsaA in Chlamydomonas reinhardtii (1995)
    Springer
    Photosynthesis research 46 (1995), S. 257-264 
    Details
    ISSN: 1573-5079
    Keywords: Chlamydomonas ; mutation ; photosynthesis ; Photosystem 1 ; PsaA ; reaction center
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The psaA and psaB genes of the chloroplast genome in oxygenic photosynthetic organisms code for the major peptides of the Photosystem 1 reaction center. A heterodimer of the two polypeptides PsaA and PsaB is thought to bind the reaction center chlorophyll, P700, and the early electron acceptors A0, A1 and Fe-SX. Fe-SX is a 4Fe4S center requiring 4 cysteine residues as ligands from the protein. As PsaA and PsaB have only three and two conserved cysteine residues respectively, it has been proposed by several groups that Fe-SX is an unusual inter-peptide center liganded by two cysteines from each peptide. This hypothesis has been tested by site directed mutagenesis of PsaA residue C575 and the adjacent D576. The C575D mutant does not assemble Photosystem 1. The C575H mutant contains a photoxidisable chlorophyll with EPR properties of P700, but no other Photosystem 1 function has been detected. The D576L mutant assembles a modified Photosystem 1 in which the EPR properties of the Fe-SA/B centers are altered. The results confirm the importance of the conserved cysteine motif region in Photosystem 1 structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020438
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