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  • 1990-1994  (41)
  • Chemistry  (32)
  • Cell & Developmental Biology  (7)
  • P700  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Detection of photosynthetic energy storage in a photosystem I reaction center preparation by photoacoustic spectroscopy (1990)
    Springer
    Photosynthesis research 24 (1990), S. 201-208 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; thermal emission ; P700 ; quantum yield ; energy conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thermal emission and photochemical energy storage were examined in photosystem I reaction center/core antenna complexes (about 40 Chl a/P700) using photoacoustic spectroscopy. Satisfactory signals could only be obtained from samples bound to hydroxyapatite and all samples had a low signal-to-noise ratio compared to either PS I or PS II in thylakoid membranes. The energy storage signal was saturated at low intensity (half saturation at 1.5 W m-2) and predicted a photochemical quantum yield of 〉90%. Exogenous donors and acceptors had no effect on the signal amplitudes indicating that energy storage is the result of charge separation between endogenous components. Fe(CN)6 -3 oxidation of P700 and dithionite-induced reduction of acceptors FA-FB inhibited energy storage. These data are compatible with the hypothesis that energy storage in PS I arises from charge separation between P700 and Fe-S centers FA-FB that is stable on the time scale of the photoacoustic modulation. High intensity background light (160 W m-2) caused an irreversible loss of energy storage and correlated with a decrease in oxidizable P700; both are probably the result of high light-induced photoinhibition. By analogy to the low fluorescence yield of PS I, the low signal-to-noise ratio in these preparations is attributed to the short lifetime of Chl singlet excited states in PS I-40 and its indirect effect on the yield of thermal emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032307
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  • 2
    Electronic Resource
    Electronic Resource
    Calculation of absolute photosystem I absorption cross-sections from P700 photo-oxidation kinetics (1991)
    Springer
    Photosynthesis research 29 (1991), S. 23-35 
    Details
    ISSN: 1573-5079
    Keywords: absorption cross-section ; P700 ; antenna size ; photosystem I ; photosynthetic unit size ; cation effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A procedure is described which permits determination of the absolute absorption cross-section of a photosynthetic unit from the kinetics of reaction center photo-oxidation under weak, continuous actinic illumination. The method was first tested on a simple model compound of known absorption cross-section. We then applied the technique to absorption cross-section and functional antenna size measurements in photosystem I (PS I). A kinetic model is presented that can be used to fit P700 photo-oxidation measurements and extract the effective photochemical rate constant. The procedure is shown to properly correct for sample scattering and for the presence of heterogeneous absorbers (pigments not functionally coupled to P700). The relevance of these corrections to comparisons of antenna size using techniques that measure ‘relative’ absorption cross-sections is discussed. Measurements on pea thylakoids in the presence and absence of 5 mM MgCl2 show a 45% increase in PS I absorption cross-section in unstacked thylakoids. Analysis of detergent-isolated ‘native’ PS I preparations (200 chlorophyll a+b/P700) clearly indicate that the preparation contains a broad distribution of antenna sizes. Finally, we confirm that Chlamydomonas reinhardtii strain LM3-A4d contains a PS I core antenna complex which binds only ∼60 chlorophyll a/P700, about half the functional size of the wild type complex. Limitations associated with calculation of functional antenna size from cross-section measurements are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00035203
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  • 3
    Electronic Resource
    Electronic Resource
    Uv resonance Raman spectroscopy of nucleic acid duplexes containing A-U and A-T base pairs (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 707-715 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Resonance Raman spectra have been obtained at several uv wavelengths (200-266 nm) for poly(rA)-poly(rU), poly(dA-dU), poly(dA)-poly(dT), and poly(dA-dT), representing nucleic acid duplexes containing A-U and A-T base pairs with different stacking interactions and different backbone conformations. Frequency shifts are seen in the exocyclic modes corresponding to coupled C4=O and C5=C6 stretching of U and T, although the NH2 scissors frequency of A is unshifted relative to that of the mononucleotide. These frequency patterns are interpreted as the superposition of H bonding and dipole-dipole coupling effects. Strong hypochromism is seen for most of the ring modes, resulting from the absorption hypochromism and from shifts in the electronic transitions due to stacking. The effects are larger for A bands in the homopolymers than in the heteropolymer duplexes, reflecting the larger influence of A/A than A/U(T) stacking. Poly(rA)-poly(rU) stands out among these polymers in showing 10 cm-1 downshifts in one U and several A modes. These shifts may be related to the A form structural parameters of this duplex, but the physical mechanism is not obvious.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290405
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  • 4
    Electronic Resource
    Electronic Resource
    Chain-Cleavage and hydrolysis of activated polyethylene glycol derivatives: Evidence for competitive processes (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 3337-3346 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies have been carried out with the tosylate of the monomethyl ether of polyethylene glycol (MeO-PEG-OTs) and with low molecular weight models to assess whether the neighboring oxygen at position 3 or 6 provides the driving force for hydrolytic cleavage of these activated derivatives. Our results reveal that MeO-PEG-OTs undergoes hydrolysis by competitive pathways. Water directly displaces the tosylate group to give the original PEG alcohol and the oxygen at position 6 nucleophilically displaces the tosylate group to give a cyclic oxonium ion as an intermediate. This intermediate can react by three pathways. First, it can lead to the production of the original PEG alcohol by attack of water on a ring carbon; second, dioxane and a lower molecular weight PEG alcohol is produced by water attack at the nonring carbon next to the charged oxygen; and third dioxane can be displaced by the oxygen atom at position 6 in the chain.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080281213
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  • 5
    Electronic Resource
    Electronic Resource
    Turbulent mixing with multiple second-order chemical reactions (1990)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 36 (1990), S. 1457-1470 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A molecular-based statistical simulation program was developed to study the covariance terms involved in the mass balance equations for complex chemical reactions during mixing. Several closure theories were compared to the simulations and available experimental data. The simple closure by Brodkey and Lewalle was found to be an extension of Toor's analysis applied to two reactions. This closure does not satisfy the molar fluctuation balance equation and was found only to represent the high Reynolds number data of Li and Toor. This result led to examining other possible closures which were based on Damkoehler numbers, reaction rate constant ratios, and limiting forms of the covariance term. These closures also were inadequate. The second reaction's covariance term varied from the product of the average values for each component to the Brodkey and Lewalle value for the range of Reynolds numbers considered.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690361002
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  • 6
    Electronic Resource
    Electronic Resource
    Quantitative determination of sulfur compounds in FCC gasolines by AED. A study of the effect of catalyst type and catalytic conditions on sulfur distribution (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 13-17 
    Details
    ISSN: 0935-6304
    Keywords: GC-AED ; Sulfur ; FCC gasoline ; Compound-independent calibration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The identification and quantification of sulfur-containing compounds in gasoline has become an area of interest because of impending legislation regulating total sulfur levels in these fuels. To study the effects of catalyst type and catalytic conditions on gasoline sulfur distribution, a method has been developed employing both the compound-independent and element-specific response of the atomic emission detector (AED). Calibration and quantification can be accomplished even where standards are not available, owing to the nature of the AED response.Compounds were separated on a thick film polydimethylsiloxane column. An external calibration curve was applied to the area responses of individual sulfur components in the sulfur chromatogram, and the concentrations of each were calculated. Summation of these sulfur concentrations over the gasoline range yields the total sulfur content of the gasoline.The method is applicable to the determination of these compounds in raw crude oils, finished gasolines, fluid cracking catalyst (FCC) unit gasolines, and fluid catalytic cracking “model” compound studies. A prefractionating column was employed to remove heavy (〉C13) materials; prefractionation is not, however, necessary for distilled or commercial gasoline samples. Detection limits, linearity, detector stability, and accuracy are discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160103
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  • 7
    Electronic Resource
    Electronic Resource
    Alteration of lacto-series glycolipid glycosyltransferase activities in human colonic adenocarcinoma DLD-1 cells after culture in N,N-dimethylformamide-containing medium (1990)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 44 (1990), S. 93-105 
    Details
    ISSN: 0730-2312
    Keywords: β1→3N-acetylglucosaminyltransferase ; cancer-associated carbohydrate antigens ; biosynthesis ; glycosphingolipid ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Human colonic adenocarcinoma DLD-1 cells were grown under conditions which induce characteristics of differentiated cells using medium containing 0.8% N,N-dimethylformamide in order to study alterations in glycosphingolipid glycosyltransferase activities during this process. Analysis of biosynthetic reactions involved in lacto-series antigen synthesis revealed no changes in the specific activities of either β1→4galactosyltransferase or α1→3/4fucosyltransferase with N,N-dimethylformamide treatment. However, a dramatic decrease of from 14- to 20-fold in the β1→3N-acetylglucosaminyltransferase activity was observed in the treated cells. This enzyme catalyzes the rate-limiting step in lacto-series core chain synthesis. This is consistent with the pattern of regulation of lacto-series antigen expression found to occur during oncogenesis in human colonic mucosa (Holmes EH, Hakomori S, Ostrander GK: J Biol Chem 262:15649, 1987). Total glycolipids from untreated and N,N-dimethylformamide-treated cells were isolated and subjected to TLC immunostain analysis and solid phase radioimmunoassay with a series of monoclonal antibodies specific for lacto-series-based carbohydrate antigens. A decrease of about 2-fold or less in the quantity of lacto-series antigens was observed as a consequence of N,N-dimethylformamide treatment in both neutral glycolipid and ganglioside fractions. The results suggest that only very low levels of β1→3N-acetylglucosaminyltransferase activity are required for the steady state expression of significant levels of lacto-series based glycolipids and that modulation of its activity levels by N,N-dimethylformamide treatment in DLD-1 cells represents a convenient in vitro system for studying aspects of regulation of lacto-series antigen expression.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240440204
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  • 8
    Electronic Resource
    Electronic Resource
    A monoclonal antibody to the T-cell receptor increases IGF-I receptor content in normal T-lymphocytes: Comparison with phytohemagglutinin (1992)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 48 (1992), S. 81-85 
    Details
    ISSN: 0730-2312
    Keywords: IGF-I receptor ; T-cells ; OKT-3 ; PHA ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The biological effects of the IGFs are mediated through interaction with specific cell surface receptors. It has been previously reported that mitogenic activation of T-lymphocytes by phytohemagglutinin (PHA) is associated with increased IGF-I receptor content. However, the mechanisms which regulate IGF-I receptor expression during T-lymphocyte activation are unknown. To explore further the regulation of IGF-I receptor expression in T-cells, we investigated IGF-I receptor content and mRNA abundance in T-lymphocytes after stimulation either by PHA or OKT-3, the latter being a monoclonal antibody directed against the CD-3 antigen of the T-cell receptor IGF-I binding in T-cells demonstrated increased IGF-I receptor content after stimulation by both PHA and OKT-3. Peak binding was induced after 72 h of treatment with PHA and 48 h of treatment with OKT-3. Affinity cross-linking of 125I-IGF-I to T-cell membranes demonstrated a single ∼ 130 kDa band which was increased after treatment with PHA or OKT-3. This band was inhibited by the addition of α-IR3, a monoclonal antibody to the IGF-I receptor. Both PHA and OKT-3 increased IGF-I receptor mRNA abundance with peak increases at 20 h and 60 h, respectively. Parallel increases in IGF-I receptor and β-actin mRNA abundance were observed, consistent with previous studies demonstrating increased actin gene expression after T-cell activation. Thus, the increase in IGF-I receptor mRNA abundance markedly preceded the increase in IGF-I receptor content after PHA stimulation, but the increase in IGF-I receptor mRNA abundance followed the increase in IGF-I receptor content after OKT-3. These studies suggest, therefore, that IGF-I receptor content in both of these activated cells is not regulated primarily at the level of steady state mRNA.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240480112
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  • 9
    Electronic Resource
    Electronic Resource
    Aberrant crypts in human colonic mucosa: Putative preneoplastic lesions (1992)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 50 (1992), S. 55-62 
    Details
    ISSN: 0730-2312
    Keywords: aberrant crypts ; chemoprevention ; enzyme-altered foci ; intermediate biomarker ; preneoplastic lesions ; putative colorectal cancer precursor ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Aberrant crypts are recognized in methylene blue-stained, unsectioned, colonic mucosa by their increased size, elliptical lumenal opening, thicker epithelial layer, and increased pericryptal region. Aberrant crypt foci in rodents are observed as early as 2 weeks and for at least 9 months after a single dose of carcinogen, have a distribution that parallels that of tumors, and have an increased number of aberrant crypts per focus with time after the carcinogen dose. The ability to quantify these lesions in the entire colon of rodents in less than an hour suggests that aberrant crypts may provide a highly efficient in vivo bioassay for colon carcinogens. Since aberrant crypt foci appear to be the earliest identifiable putative precursors of colon cancer, they represent lesions that can be characterized further for the earliest genetic and biochemical alterations. In F344 rats, we have demonstrated that aberrant crypts have multiple histochemically-detectable enzyme alterations. Using similar techniques, we were the first to demonstrate aberrant crypts in unsectioned human mucosa. After embedding and sectioning, these microscopic aberrant crypts resemble rare lesions described earlier in the literature after extensive serial sectioning. In rats and humans, aberrant crypts may be histologically normal or display varying degrees of dysplasia and histochemically-detectable altered enzyme activities. These putative, preneoplastic lesions should reveal early changes that precede colon cancer and ways to alter their progression.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240501111
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  • 10
    Electronic Resource
    Electronic Resource
    Stable expression of a cDNA encoding a human β1 → 3galactosyltransferase responsible for lacto-series type 1 core chain synthesis in non-expressing cells: Variation in the nature of cell surface antigens expressed (1992)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 50 (1992), S. 165-177 
    Details
    ISSN: 0730-2312
    Keywords: β1 → 3galactosyltransferase ; stable expression ; glycolipids ; lacto-series type 1 chain ; Lewis antigens ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Transient expression of a human colonic adenocarcinoma Colo 205 cell derived cDNA in cell lines which ordinarily express only neolacto-series glycolipids has resulted in the expression of a β1 → 3galactosyltransferase gene responsible for synthesis of glycolipids based upon the lacto-series type 1 core chain. Calcium phosphate transfected cells were panned on anti-lgM coated plates after initial treatment with a combination of monoclonal antibodies specific for type 1 chain terminal structures (TE-3) and a very broadly specific antibody reactive with multiple type 1 chain derivatives (TE-2). Adherent cells after panning were capable of efficiently transferring Gal in β1 → 3-linkage to the acceptor glycolipid Lc3. Using these reagents, clones of stably transfected human colonic adenocarcinoma HCT-15 cells were produced and isolated. Parental HCT-15 cells do not express type 1 chain based antigens. The nature of the type 1 chain based antigens produced in each of these clones was analyzed by solid phase antibody binding assays. Three types of behavior were observed. Formation of type 1 terminal structures that were either exclusively sialylated or fucosylated, or a mixture of sialylated and fucosylated determinants occurred. In contrast, no difference in type 2 antigen expression between any clone and the parental cells was observed. These data suggest that coordination of subsequent reactions capable of modifying type 1 chain structures is not the same in all clones. The relationship of these results to aspects of cellular regulation of carbohydrate biosynthesis is discussed. © 1992 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240500207
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