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  • 11
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 11 (1972), S. 1822-1827 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 110 (2000), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Homology modeling has been used to identify extra-chloroplastic enzymes that contain potential disulfide bonds. All of the higher plant fructose bisphosphatases and mitochondrial citrate synthases that have been tested to date, two glyceraldehyde-3-P dehydrogenases, two enolases and one lactate dehydrogenase, are redox-sensitive and may then be redox-regulated in vivo. Apparently, redox-sensitivity is not limited to the chloroplast.
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Reaction centres of R. viridis were prepared using the method described by den Blanken et al.3. The reaction centres had an optical absorbance ratio ?280/?83? = 2.6. SDS-polyacrylamide gel electrophoresis showed that the reaction centres consist of four types of protein subunit4'5. The ...
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature structural biology 2 (1995), S. 1057-1059 
    ISSN: 1072-8368
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Sir—The bacterial photosynthetic reaction centre is an intrinsic membrane protein which converts light excitation energy into chemical free energy. This process is accomplished through a light-induced transmembrane charge separation between a dimer of bacteriochloro-phyll (P) situated near ...
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Immunogenetics 35 (1992), S. 224-234 
    ISSN: 1432-1211
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract T-cell receptor (Tcr) α chains are classified into four subgroups (I, II, III, and miscellaneous) based on the amino acid residues at positions 61 and 62. Subgroup I has Gly Phe at these positions, subgroup II has Arg Phe, subgroup III has Arg Leu, and subgroup miscellaneous has several other combinations. Variability plots for subgroups I, II, and III sequences show higher values around positions 93–103, 105, 108, 111, 113, and 115, suggesting that these positions may interact with the processed antigen molecules. Smaller peaks are present at various other regions which may bind the major histocompatibility complex class I or II molecules. The patterns of variability within one subgroup are similar for all species, for human alone, and for mouse alone. These subgroup patterns appear much less complicated than patterns for sequences in all subgroups taken together, implying that subgroups may be related to Tcr functions. Among 83 mouse chains, 15 are from cytotoxic cells and 40 from helper cells. Of the 15 from cytotoxic cells, 11, 2, 0, and 2 are in subgroups I, II, III, and miscellaneous; and of the 40 from helper cells, 9, 16, 12, ans 3 are in subgroups I, II, III, and miscellaneous, respectively. Thus, a correlation between sequence and function of Tcr α chains seems possible.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 1573-5079
    Keywords: electron paramagnetic resonance ; electron spin polarization ; quinone binding ; revertant isolation ; electrostatics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Site-specific mutations in the quinone binding sites of the photosynthetic reaction center (RC) protein complexes of Rhodobacter (R.) capsulatus caused pronounced effects on sequential electron transfer. Conserved residues that break the twofold symmetry in this region of the RC – M246Ala and M247Ala in the QA binding pocket, and L212Glu and L213Asp in the QB binding pocket – were targeted. We constructed a QB-site mutant, L212Glu-L213Asp → Ala-Ala, and a QA-site mutant, M246Ala–M247Ala → Glu-Asp, to partially balance the differences in charge distribution normally found between the two quinone binding sites. In addition, two photocompetent revertants were isolated from the photosynthetically-incompetent M246Glu-M247Asp mutant: M246Ala–M247Asp and M246Gly–M247Asp. Sequential electron transfer was investigated by continuous light excitation and time-resolved electron paramagnetic resonance (EPR), and time-resolved optical techniques. Several lines of EPR evidence suggested that the forward electron transfer rate to QA, kQ, was slowed in those strains containing altered QA sites. The slower rates of secondary electron transfer were confirmed by time-resolved optical results with the M246Glu-M247Asp mutations in the QA site resulting in a dramatically lowered secondary electron transfer efficiency [kQ 〈 (2 ns)-1] in comparison with either the native R. capsulatus RC or the QB site mutant [kQ ≈ (200 ps)-1]. Secondary electron transfer in the two revertants was intermediate between that of the native RC and the QA mutant. The P+ QA- → PQA charge recombination rates were also changed in the strains that carried altered QA sites. We show that local mutations in the QA site, presumably through local electrostatic changes, significantly alter binding and electron transfer properties of QA.
    Type of Medium: Electronic Resource
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  • 17
    ISSN: 1573-5079
    Keywords: electron transfer ; proton transfer ; photosynthesis ; quinone ; reaction center ; site-specific mutagenesis ; suppressor mutations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two acidic residues, L212Glu and L213Asp, in the QB binding sites of the photosynthetic reaction centers of Rhodobacter capsulatus and Rhodobacter sphaeroides are thought to play central roles in the transfer of protons to the quinone anion(s) generated by photoinduced electron transfer. We constructed the site-specific double mutant L212Ala-L213Ala in R. capsulatus, that is incapable of growth under photosynthetic conditions. A photocompetent derivative of that strain has been isolated that carries the original L212Ala-L213Ala double mutation and a second-site suppressor mutation at residue M43 (Asn→Asp), outside of the QB binding site, that is solely responsible for restoring the photosynthetic phenotype. The Asp,Asn combination of residues at the L213 and M43 positions is conserved in the five species of photosynthetic bacteria whose reaction center sequences are known. In R. capsulatus and R. sphaeroides, the pair is L213Asp-M43Asn. But, the reaction centers of Rhodopseudomonas viridis, Rhodospirillum rubrum and Chloroflexus aurantiacus reverse the combination to L213Asn-M43Asp. In this respect, the QB site of the suppressor strain resembles that of the latter three species in that it couples an uncharged residue at L213 with an acidic residue at M43. These reaction centers, in which L213 is an amide, must employ an alternative proton transfer pathway. The observation that the M43Asn→Asp mutation in R. capsulatus compensates for the loss of both acidic residues at L212 and L213 suggests that M43Asp is involved in a new proton transfer route in this species that resembles the one normally used in reaction centers of Rps. virddis, Rsp. rubrum and C. aurantiacus.
    Type of Medium: Electronic Resource
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  • 18
    ISSN: 1573-5079
    Keywords: electron transfer ; phenotypic revertants ; photosynthesis ; proton transfer ; site-specific mutagenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To probe the structural elements that contribute to the functional asymmetries of the two ubiquinone10 binding pockets in the reaction center of Rhodobacter capsulatus, we targeted the L212Glu–L213Asp (near QB) and the M246Ala-M247Ala (near QA) pairs of symmetry-related residues for site-specific mutagenesis. We have constructed site-specific mutants that eliminate the sequence differences at these positions (L212Glu–L213Asp→Ala-Ala or M246Ala–M247Ala→Glu-Asp), and have reversed that asymmetry by constructing a quadruple-mutant strain, ‘RQ’ (L212Glu–L213Asp-M246Ala–M247Ala→Ala-Ala-Gl u-Asp). The mutations were designed to change the charge distribution in the quinone-binding region of the reaction center; none of the strains is capable of photosynthetic growth. In photocompetent phenotypic revertants of the RQ strain, second-site mutations which affect QB function are coupled to mutations in the QA site which restore an Ala or substitute a Tyr at the M247 site; one strain carries an additional Met→Leu substitution at M260 near QA. All of the RQ revertants retain the engineered M246Ala→Glu mutation in the QA site as well as the L212Ala–L213Ala mutations in the QB site. Kinetic characterization of the RQ revertants will give us an idea of what structural and functional elements are important for restoring efficiency to electron and proton transfer pathways in the RQ RC, which is far from native. To date, these preliminary results underscore the importance of an asymmetric distribution of polar amino acids in the quinone binding pockets and its influence on the functional properties of the reaction center.
    Type of Medium: Electronic Resource
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