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  • 1
    ISSN: 1617-4623
    Keywords: Random cartridge mutagenesis ; Transformation ; Recombination ; Genetic mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Photosynthetic mutants of the cyanobacterium Synechocystis PCC 6803 were produced by a random cartridge mutagenesis method leading to gene inactivation. This procedure relies on random ligation of an Escherichia coli kanamycin resistance (Kmr) gene to restriction fragments of genomic DNA from the host. Then recombination occurring during transformation promotes integration of the marker gene into the genome of the recipient cells. Several mutants impaired in photosynthesis were obtained by this procedure. All are partially or totally defective in photosystem II activity and some of them also harbour a functionally modified photosystem I. Restriction and recombination data showed that one mutant (AK1) is best explained as an insertion of the Kmr gene into an AvaII restriction site of the gene psbD-1. All other harbour a deletion, ranging from at least 1.15 kb (AK3) to more than 50 kb (AK9), which partly or fully overlaps the genes psbB and/or psbD-1, depending on the mutant. A genetic-physical map of the more than 60 kb region of the cyanobacterial genome harbouring the genes psbB, psbC and psbD-1 was constructed by combining published sequence data on these genes with the results of recombination and restriction mapping.
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  • 2
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence lifetime ; K2IrCl6 quenching ; light harvesting complex ; Photosystem 2 heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To understand the origins of the different lifetime components of photosystem 2 (PS2) chlorophyll (Chl) fluorescence we have studied their susceptibility to potassium iridic chloride (K2IrCl6) which has been shown to bleach antenna pigments of photosynthetic bacteria (Loach et al. 1963). The addition of K2IrCl6 to PS2 particles gives rise to a preferential quenching of the variable Chl fluorescence (Fv). At concentrations lower than 20 μM, this is brought about mainly by a decrease in the yield, but not in the lifetime, of the slowest component when all the PS2 reaction centres are closed (FM). The yield of the middle and fast decays are not significantly altered. This type of quenching is not seen with DNB. The iridate-induced quenching of the initial fluorescence level (F0) is due to a proportional decrease in the yield and lifetime of the three components and correlates with the observed modification in the relative quantum yield of oxygen evolution. In this concentration range a bleaching of Chl a is seen. At higher iridate levels, greater than 20 μM, a proportional decrease in the lifetimes and yields of the three kinetic components is seen at FM. These changes are associated with a carotenoid bleaching. In isolated light harvesting Chl a/b complexes of PS2 (LHC2), iridate addition converts a 4 ns decay into a 200 ps emission and both types of bleaching are observed. By also measuring the rate of PS2 trap closure versus iridate concentration, we have discussed the results in terms of excitation energy transfer.
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  • 3
    ISSN: 1573-5079
    Keywords: oxygen evolution ; Ca2+ ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A number of recent reports have concluded that Ca2+ is not released by treatments which are usually thought to induce the depletion of Ca2+. Consequently, it was proposed that the Ca2+ demand was not related to a specific rôle for Ca2+ in Photosystem-II oxygen evolution. In this letter, we scrutinize the data behind these conclusions and argue that, based on these data, it is premature to question the view that intrinsic Ca2+ is actually being released.
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  • 4
    ISSN: 1432-2242
    Keywords: Mitchondrial DNA ; Chloroplast DNA ; DNA polymorphism ; Cytoplasmic male sterility ; Onion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mitochondrial and chloroplast DNA was isolated from fertile and cytoplasmic male sterile cultivars of cultivated onions. Restriction fragment length polymorphism led to the distinction between cytoplasms S and M. Mitochondrial DNA patterns from S cytoplasms appeared dentical and characterized mostly male sterile lines. An open-pollinated variety was found to bear this cytoplasm and thought to be the origin of S types. Mitochondrial DNA patterns from M cytoplasms were subdivided into four types, M1 and M2 corresponding to normal N cytoplasm, M3 and M4 probably corresponding to T cytoplasms. S and M cytoplasms were also distinguished by chloroplast DNA restriction patterns. Our results confirm previous genetic distinction between S, N and T cytoplasms.
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  • 5
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: The oxidized radicals of aromatic amino acids, 4-methylimidazole and phenol were generated by UV irradiation at low temperature. The radicals were monitored by EPR spectroscopy. For the first time, infrared (IR) modes characteristic of the tyrosine, tryptophan, phenylalanine, and histidine radicals were obtained by FTIR difference spectroscopy between the ground state and the radical state. The effects of D- (on Tyr and phenol) or 15N- (on His) labeling on the IR modes of the radicals were studied, as were the influence of hydrogen bonding and of pH. These parameters were studied to model the possible radical structures and environments in proteins. The radicals obtained with tyrosine, phenol, and 4-ethylphenol present six main IR modes: a combination mode at ∼ 2110-2106 cm-1; the v8b(CC) mode at 1550-1556 cm-1, the v7a(CO) and v19b(CC) modes both at 1515-1500 cm-1, which are distinctly affected by D-labeling of the phenol ring; the 14(vCC + δCH) mode at 1290-1288 cm-1, which is strongly modified when the radical is hydrogen bonded; and the 9a(CC) mode at 1163-1159 cm-1. These IR modes partly confirm the assignments made by resonance Raman (RR) spectroscopy and should help to obtain precise structure and force field calculations for the radicals. The deprotonated 4-methylimidazole radical (4-MeIm·) is obtained at pH 12. It has characteristic IR modes at 1593 v(CC), 1425 δCH3, 1376 δCH3, 1315 cm-1, 1213 cm-1 and 1098 cm-1 δ(CH). The methyl modes seem strongly downshifted upon radical formation, while the ring modes appear less affected. In particular, the C4C5 double-bond character is conserved. The protonated 4-methylimidazole radical formed at pH ≤ 6 is characterized by signals at 1433 cm-1, 1380 cm-1, 1310 cm-1, 1227 cm-1, and 1172 cm-1. The histidine and tyrosine radicals present similar IR modes as the corresponding model of their sidechain. For all the amino acids, the vas(COO-) and vs(COO-) modes of the terminal carboxylate were respectively up- and downshifted by ∼ 20 cm-1 upon the radical formation. This effect suggests that, in a protein, the amide bond of the amino acid could also be influenced by the radical formation. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 6
    ISSN: 1434-1948
    Keywords: Manganese ; EPR spectroscopy ; Spectroelectrochemistry ; Mixed-valent compounds ; Tripodal ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and structural characterization of the novel [MnIII,IV2O2(N,Nbispicen)2](ClO4)3·CH3CN complex employing the tetradentate ligand N,Nbispicen = N,N-bis(2-pyridylmethyl)-1,2-diaminoethane are reported. Magnetic properties were determined and show that the ground state is a spin doublet. This can be quantitatively interpreted by antiferromagnetic coupling between a Mn(III) high spin and a Mn(IV) (J = -316 cm-1). The 16 line solution EPR spectrum exhibits an unusual splitting in the low field resonances. The following rhombic tensors were needed to simulate the EPR spectrum: |A1x|= 160 10-4 cm-1, |A1y| = 144 10-4 cm-1, |A1z|= 109 10-4 cm-1, |A2x|= 69 10-4 cm-1, |A2y| = 72 10-4 cm-1, |A2z| = 75 10-4 cm-1, gx = 2.001, gy = 1.996, gz = 1.984. The classical ligand field theory of local [gIII] and [gIV] tensors implemented with the first order perturbation theory to describe the properties of the pair does not result in a satisfying description of the [g1/2] tensor unless a large reduction in the spin-orbit constant is invoked. A simplified version of second-order perturbation theory leads to effects in qualitative agreement with experiment but weak as expected from the large |J| value. The magnitude of these effects depends, however, on the anisotropy effects on each Mn ion. It is suggested that determination of the anisotropy of the magnetic properties of the monomeric Mn(III) and Mn(IV) moieties would be a valuable goal for a future study of these mixed valent dimanganese-di-μ-oxo complexes. The complex exhibits two quasi-reversible waves in the cyclic voltammogram, one at E1/2 = 0.18 V vs SCE for the III/IV █ III/III couple and the other at E1/2 = 0.98 V vs SCE for the III/IV █ IV/IV couple. The UV-Vis spectra of the three redox states have been recorded spectroelectrochemically.
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  • 7
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Ytterbium (Yb3+) vibronic sideband (VSB) spectroscopy allows the identification of the lanthanide ligands both in model compounds and in Yb3+ -reconstituted metalloproteins. In some cases there exist multiple binding sites which complicate the Yb3+ fluorescence spectrum. The presence of different sites can be deduced from the variation of the intensity of the VBSs, when the wavelength of excitation is varied. A general two-dimensional (2D) correlation method developed by Noda can be potentially used to discriminate the different Yb3+ binding sites. A very simple procedure has been further developed so that, by using a few different spectra, usable information can be extracted from the 2D spectrum; the spectra were obtained with different wavelengths of excitation. This method is applied successfully in the present work on Yb3+-reconstituted transferrin, which contains two spectroscopically different Yb3+ sites, in order to determine any structural difference between the two sites. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 8
    ISSN: 1434-1948
    Keywords: Peroxo complexes ; Iron ; Nonheme iron ; Iron ; EPR spectroscopy ; Mass spectrometry ; UV/Vis spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some nonheme hydroperoxoiron(III) species have been recently characterized by several groups. The reported examples were obtained by adding H2O2 in excess to an FeII complex with a neutral polypyridine ligand. We show here that on deprotonation, the purple low-spin hydroperoxoiron(III) complex [L5FeIIIOOH]2+ [L5 = N-methyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine] gives a blue high-spin species which we characterized as the η2-peroxoiron(III) species [L5FeIIIO2]+. It seems that with such an auxiliary ligand, the hydroperoxo group is acidic in contrast with its basicity when it is coordinated to a heme group.
    Additional Material: 3 Ill.
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  • 9
    ISSN: 0005-2728
    Keywords: (Pea and lettuce chloroplast) ; Chlorophyll fluorescence ; Electron transfer ; Photosynthesis ; Photosystem II ; Protein phosphorylation
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0005-2728
    Keywords: (Spinach) ; Oxygen evolution ; Photosynthesis ; Photosystem II ; S-state transition
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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