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  • Organic Chemistry  (23)
  • Autoradiography  (6)
  • Photosystem II  (5)
  • 1
    Electronic Resource
    Electronic Resource
    The primary processes of photosystem II in purified guard-cell protoplasts and mesophyll-cell protoplasts from Commelina communis L. (1983)
    Springer
    Planta 159 (1983), S. 554-560 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Commelina ; Guard cell ; Oxygen evolution (guard cell) ; Photosystem II ; Protoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Guard-cell protoplasts were isolated by enzymic digestion of the epidermis peeled from the abaxial surface of leaves from Commelina communis L. The protoplasts were separated from mesophyll-cell protoplasts and other contaminants by density-gradient centrifugation, and the purity of the preparations carefully and quantitatively assessed by light microscopy. The preparations of guard-cell protoplasts were then compared with mesophyll-cell protoplasts in terms of the activity of photosystem II as assessed by a) the light-induced evolution of oxygen under both steady-state and flashing light and b) the characteristics of photosystem-II chlorophyll fluorescence. In all experiments, clear photosystem-II activity was found in guard-cell protoplasts, although some subtle distinctions between guard-cell and mesophyll-cell protoplasts were found. The contribution of any contaimination by mesophyll-cell chlorophyll to guard-cell-protoplast signals was estimated to be less than 3% in all cases. The results indicate that photosystem II is present and active in guard cells of Commelina.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409145
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  • 2
    Electronic Resource
    Electronic Resource
    Uptake and retention of3H-estradiol by gonadotrophs and lactotrophs in the pituitary glands of the guinea pig, hamster and gerbil (1987)
    Springer
    Cell & tissue research 248 (1987), S. 75-78 
    Details
    ISSN: 1432-0878
    Keywords: LH-cells ; Prolactin cells ; Immunocytochemistry ; Estrogen ; Autoradiography ; Guinea pig ; Hamster ; Gerbil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Nuclear uptake and retention of3H-estradiol by luteinizing hormone (LH) and prolactin (PRL) cells was examined in three species of rodents (guinea pigs, hamsters and gerbils) using the combined techniques of immunocyto-chemistry and autoradiography. Castrated animals were injected with3H-estradiol and decapitated 1.5 h later. The pituitary glands were processed for thaw-mount autoradiography followed by conventional immunocytochemical staining for LH and PRL.3H-estradiol accumulated in more than 80% of the anterior pituitary cells in the gerbils, while only 33 and 22% of the cells accumulated3H-estradiol in the hamsters and guinea pigs, respectively. A varying percentage of immunoreactive LH and PRL cells in all three species were found also to contain binding sites for estradiol. Some LH and PRL cells in hamsters and guinea pigs and only some in PRL cells of gerbils were found to be devoid of grains. Quantitative analysis revealed that the number of grains per nucleus differed considerably from cell to cell. LH cells of guinea pigs accumulated much larger amounts of3H-estradiol than did the PRL cells, while the LH cells in the hamsters and gerbils accumulated only slightly more3H-estradiol than the PRL cells. These results confirm the previous observations in rats and baboons that demonstrated tremendous species differences in percentage of cells in the anterior pituitary gland that accumulated3H-estradiol. Also, these data suggest that there are functionally heterogeneous cell types among the LH and PRL cells in hamsters, guinea pigs and gerbils as has been previously demonstrated in rats and baboons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01239965
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  • 3
    Electronic Resource
    Electronic Resource
    Flash-induced redox changes in oxygen-evolving spinach Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 169-176 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen-evolving complex ; UV asorbance changes ; EPR signal II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flash-induced redox reactions in spinach PS II core particles were investigated with absorbance difference spectroscopy in the UV-region and EPR spectroscopy. In the absence of artificial electron acceptors, electron transport was limited to a single turnover. Addition of the electron acceptors DCBQ and ferricyanide restored the characteristic period-four oscillation in the UV absorbance associated with the S-state cycle, but not the period-two oscillation indicative of the alternating appearance and disappearance of a semiquinone at the QB-site. In contrast to PS II membranes, all active centers were in state S1 after dark adaptation. The absorbance increase associated with the S-state transitions on the first two flashes, attributed to the Z+S1→ZS2 and Z+S2→ZS3 transitions, respectively, had half-times of 95 and 380 μs, similar to those reported for PS II membrane fragments. The decrease due to the Z+S3→ZS0 transition on the third flash had a half-time of 4.5 ms, as in salt-washed PS II membrane fragments. On the fourth flash a small, unresolved, increase of less than 3 μs was observed, which might be due to the Z+S0→ZS1 transition. The deactivation of the higher S-states was unusually fast and occurred within a few seconds and so was the oxidation of S0 to S1 in the dark, which had a half-time of 2–3 min. The same lifetime was found for tyrosine D+, which appeared to be formed within milliseconds after the first flash in about 10% inactive centers and after the third and later flashes by active centers in Z+S3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146416
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  • 4
    Electronic Resource
    Electronic Resource
    Degradation of the Photosystem II D1 and D2 proteins in different strains of the cyanobacterium Synechocystis PCC 6803 varying with respect to the type and level of psbA transcript (2000)
    Springer
    Plant molecular biology 42 (2000), S. 635-645 
    Details
    ISSN: 1573-5028
    Keywords: cyanobacteria ; D1 ; D2 ; Photosystem II ; psbA ; Synechocystis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The turnover of the D1 and D2 proteins of Photosystem II (PSII) has been investigated by pulse-chase radiolabeling in several strains of the cyanobacterium Synechocystis PCC 6803 containing different types and levels of the psbA transcript. Strains lacking psbA1 and psbA3 gene and containing high levels of the psbA2 transcript showed the selective synthesis of D1 whose degradation could be slowed down by the protein synthesis inhibitor lincomycin. In contrast, in strains containing just the psbA3 gene, the intensity of the D1 protein labeling was lower and labeling of the D2 and CP43 proteins was stimulated in comparison to the psbA2-containing strains. In addition, the rate and selectivity of the D1 degradation and its dependence on the presence of lincomycin was proportional to the level of the psbA3 transcript in the particular strain. Consequently, there was parallel, lincomycin-independent and slowed-down breakdown of the D1 and D2 proteins in strains with the lowest level of psbA3 transcript. These results are discussed in terms of a model in which the rate of D1 and D2 degradation in cyanobacteria is affected not only by the rate of PSII photodamage, but also by the availability of newly synthesized D1 protein. Moreover, the comparison of the non-oxygen-evolving D1 mutants D170A** and Y161F*** differing by the presence of tyrosine Z has indicated a minor role of the oxidized form of this secondary PSII electron donor in the donor side mechanism of D1 and D2 protein breakdown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006305308196
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  • 5
    Electronic Resource
    Electronic Resource
    CO2 and O2 dependence of PS II activity in C4 plants having genetically produced deficiencies in the C3 or C4 cycle (1998)
    Springer
    Photosynthesis research 58 (1998), S. 91-101 
    Details
    ISSN: 1573-5079
    Keywords: C4 photosynthesis ; PEP carboxylase mutants ; Photosystem II ; Rubisco transgenic plants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The CO2 dependence of rates of CO2 fixation (A) and photochemistry of PS II at 5, 15 and 30% O2 were analyzed in the C4 plant Amaranthus edulis having a C4 cycle deficiency [phosphoenolpyruvate carboxylase (PEPC) mutants], and in the C4 plant Flaveria bidentis having a C3 cycle deficiency [Rubisco small subunit antisense (αSSU)]. In the wild type (WT) A. edulis and its heterozygous mutant having less than 50% WT PEPC activity there was a similar dependence of A and PS II photochemistry on varying CO2, although the CO2 saturated rates were 25% lower in heterozygous plants. The homozygous plants having less than 2% PEPC of the WT had significant levels of photorespiration at ambient levels of CO2 and required about 30 times ambient levels for maximum rates of A. Despite variation in the capacity of the C4 cycle, more than 91% of PS II activity was linearly associated with A under varying CO2 at 5, 15 and 30% O2. However, the WT plant had a higher PS II activity per CO2 fixed under saturating CO2 than the homozygous mutant, which is suggested to be due to elimination of the C4 cycle and its associated requirement for ATP from a Mehler reaction. In the αSSU F. bidentis plants, a decreased rate of A (35%) and PS II activity (33%) accompanied a decrease in Rubisco capacity. There was some increase in alternative electron sinks at high CO2 when the C3 cycle was constrained, which may be due to increased flux through the C4 cycle via an ATP generating Mehler reaction. Nevertheless, even with constraints on the function of the C4 or C3 cycle by genetic modifications, analyses of CO2 response curves under varying levels of O2 indicate that CO2 assimilation is the main determinant of PS II activity in C4 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006176713574
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  • 6
    Electronic Resource
    Electronic Resource
    Absorbance difference spectra of the S-state transitions in Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 323-330 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen evolving complex ; UV absorbance changes ; S-state spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Redox changes of the oxygen evolving complex in PS II core particles were investigated by absorbance difference spectroscopy in the UV-region. The oscillation of the absorbance changes induced by a series of saturating flashes could not be explained by the minimal Kok model (Kok et al. 1970) consisting of a 4-step redox cycle, S0 → S1 → S2 → S3 → S0, although the values of most of the relevant parameters had been determined experimentally. Additional assumptions which allow a consistent fit of all data are a slow equilibration of the S3 state with an inactive state, perhaps related to Ca2+-release, and a low quantum efficiency for the first turnover after dark-adaptation. Difference spectra of the successive S-state transitions were determined. At wavelengths above 370 nm, they were very different due to the different contribution of a Chl bandshift in each spectrum. At shorter wavelengths, the S1 → S2 transition showed a difference spectrum similar to that reported by Dekker et al. 1984b and attributed to an Mn(III) to Mn(IV) oxidation. The spectrum of absorbance changes associated with the S2 → S3 transition was similar to that reported by Lavergne 1991 for PS II membranes. The S0 → S1 transition was associated with a smaller but still substantial absorbance increase in the UV. Differences with the spectra reported by Lavergne 1991 are attributed to electrostatic effects on electron transfer at the acceptor side associated with the S-state dependence of proton release in PS II membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046757
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  • 7
    Electronic Resource
    Electronic Resource
    Spectrophotometric and Nuclear Magnetic Resonance Study of Temperature- and Pressure-induced Changes in the Intimate Solvation of Neodymium (III) in N, N-Dimethylformamide and Trimethylphosphate (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 1025-1028 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature- and pressure-dependent equilibria for the addition of an extra N, N-dimethylforrnamide (DMF) or trimethylphosphate (TMP) ligand onto [Nd (DMF)8]3+- and [Nd(TMP)6]3+-species respectively have been measured by visible spectrophotometry. Complementary NMR. studies on other lanthanide ions show a gradual shift in preference for the lower coordination number across the lanthanide series.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650333
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of Linear Oligomers of (R)-3-Hydroxybutyrate and Solid-State Structural Investigations by electron microscopy and X-ray scatteringDedicated to Prof. Dr. H. Ringsdorf on the occasion of his 65th birthday (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1099-1123 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Repetitive treatment of the biopolymer P(3-HB) (molecular weight 〉 105 Dalton, storage or s-P(3-HB)), with lithium hexamethyl disilazanid (LHMDS) at -70° in THF leads to a mixture of oligomers with increasingly sharp distribution around a 15-, 30-, and 45mer. Discrete fragments are also isolated when P(3-HB) is heated under reflux (89°) in neat Et3N. Linear oligo(3-HB) derivatives (3-7) containing up to 96 3-HB units are synthesized using an exponential segment-coupling strategy. These oligomers are used to calibrate size-exclusion chromatography columns for the analysis of oligo(3-HB) samples from the different sources. The linear oligo-(3-HB) derivatives also served as a model with respect to the physical properties of high molecular weight P(3-HB) and were investigated as such by transmission electron microscopy (TEM) and by small- and wide-angle X-ray scattering (SAXS and WAXS). The thicknesses of the lamellar crystallites (long periods) formed by the 8mer, 16mer, and 32mer, are ca. 26, 52, and 53 Å, respectively, indicating that the 32mer molecules are folded once, very tightly, into a ‘hair-pin’-type conformation. High-molecular-weight P(3-HB), which was crystallized in a similar way, also has a lamellar crystallite thickness of ca. 50-65 Å. Thus, the treatment of P(3-HB) with LHMDS at low temperature causes etching of the amorphous regions, an effect well known in polymer science for studying the regularity of chain folding. The ca. 50-Å packing within the tight folds of P(3-HB) is discussed in view of its possible function in ion transport through cell membranes.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770423
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  • 9
    Electronic Resource
    Electronic Resource
    High-Pressure Stopped-Flow Study of the Kinetics of Base Hydrolysis of the Dichromate Ion by Hydroxide Ion, Ammonia, Water, and 2,6-Lutidine in Aqueous Solution (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2445-2448 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Volumes of activation for the base hydrolysis of the dichromate anion have been measured at 298.2 K, using high-pressure stopped-flow spectrophotometry. The values of ΔV* (cm3 · mol-1), - 17.9 ± 0.6, - 19.2 ± 0.9, - 24.9 ± 0.9 and - 26.0 ± 0.7 for OH-, NH3, H2O and 2,6-lutidine, respectively, are consistent with an interchange mechanism with associative activation mode (Ia).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660809
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  • 10
    Electronic Resource
    Electronic Resource
    Dendrimers with Porphyrin Cores: Synthetic models for globular heme proteins (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1773-1801 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dendritic iron porphyrins were synthesized as functional mimics of globular electron-transfer heme proteins. The cascade molecules 1 · Zn-3 Zn of first to third generation were obtained starting from the (meso-diarylporphyrin) zinc 6 · Zn which contains four carboxylate arms for attachment of the poly(ether-amide) dendritic branches by peptide-coupling methodology (Scheme 1). Generation 3 compound 3 · Zn with 108 methyl-carboxylate end groups has a molecular weight of 19054. D, and computer modeling suggests that its structure is globular and densely-packed, measuring ca. 4 nm in diameter and, therefore, similar in dimensions to the electron-transfer protein cytochrome-c. Starting from the generation 1 poly(carboxylic acid) 11 · Zn and the generation 2 analog 12 · Zn the dendritic ZnII porphyrins 4 · Zn and 5 · Zn, respectively, were obtained by esterification with triethyleneglycol monomethyl ether (Schemes 3 and 4). Demetallation followed by insertion of FeII and in situ oxidation afforded the water-soluble dendritic iron porphyrins 4 FeCl and 5 FeCl. The electrochemical behavior of esters 1 · Zn-3 · Zn in organic solvents changed smoothly with increasing dendritic generation (Table 1). Progressing from 1 · Zn to 3 · Zn in THF, the first porphyrin-centered oxidation and reduction potentials become more negative by 320 and 210mV, respectively. These changes were attributed to strong microenvironmental effects imposed on the electroactive core by the densely packed dendritic surroundings. The electrochemical properties of 4 · FeCl and 5 · FeCl were investigated by cyclic voltammetry in both CH2Cl2 and H2O (Tables 2 and 3). Progressing from 4 · FeCl to 5 · FeCl in CH2Cl2, the redox potential of the biologically relevant FeIII/FeII couple remained virtually unchanged, whereas in aqueous solution, 5 FeCl exhibited a potential 420 mV more positive than did 4 FeCl. The large difference between these potentials in H2O was attributed to differences in solvation of the core electrophore. Whereas the relatively open dendritic branches in 4 · Fecl do not impede access of bulk solvent to the central core, the densely packed dendritic superstructure of 5 · FeCl significantly reduces contact between the heme and external solvent. As a result, the more charged FeIII state is destabilized relative to FeII, and the redox potential is strongly shifted to a more positive value.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800603
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