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  • 1
    Electronic Resource
    Electronic Resource
    MODELING THE PERFORMANCE OF DEEP WASTE STABILIZATION PONDS (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 24 (1988), S. 0 
    Details
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The performance characteristics of a deep waste stabilization pond operating in Southeast Spain were studied for one year; the results show a high reduction in organic load and nutrients, as well as disinfection of the effluent, after a retention time that varies as a function of climatic conditions. Mathematical models describing its hydraulic, thermal, and biochemical bahavior are presented and compared with a set of measured data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1752-1688.1988.tb02996.x
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  • 2
    Electronic Resource
    Electronic Resource
    Proteolysis of ribulose-1,5-bisphosphate carboxylase/oxygenase in Citrus leaf extracts (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 66 (1986), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) has been purified from orange [Citrus sinensis (L.) Osbeck cv. Washington Navel] leaves using sucrose gradient centrifugation in a fixed angle rotor. Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two major bands corresponding to the two subunits of RuBP carboxylase were found. The large subunit coincided with the polypeptide band that has been previously reported to be preferentially mobilized during the spring and summer flush periods.The degradation of RuBP carboxylase during autodigestion of Citrus leaf extracts, investigated by SDS-PAGE, occurred mainly at acidic (2.5-5.5) pH. The two subunits showed differences in the rate of degradation, the smaller being more rapidly hydrolyzed than the larger. At least four proteolytic activities were identified by means of inhibitor experiments: 1) a pepstatin A-sensitive activity that acts on both RuBP carboxylase subunits, 2) a mercurial (p-hydroxymercuribenzoate and p-chloromercuriphenylsulfonate)-sensitive activity that degrades only the small subunit, 3) an EDTA-sensitive activity that hydrolyzes both the large and small subunits, and 4) a mercurial-stimulated activity that acts only on the large subunit. It is suggested that the last two proteases may be responsible for the degradation of RuBP carboxylase observed in vivo during the periods of mobilization of leaf protein in Citrus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1986.tb05938.x
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  • 3
    Electronic Resource
    Electronic Resource
    Extraction of tracheal sap from Citrus and analysis of its nitrogenous compounds (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 50 (1980), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Tracheal sap was extracted from sections of stems (0.5 to 1.5 cm in diameter and 7.5 to 15.0 cm in length) of orange trees (Citrus sinensis (L.) Osbeck cv. Washington Navel) by using a combination of the vacuum and liquid displacement methods. The volume of sap obtained and its concentration of nitrogenous compounds were dependent on the volume of displacing liquid used for the extraction. Four ml of water-saturated 1-butanol extracted essentially all of the xylem fluid present in the stem sections without apparent production of artifacts.The time of sampling affected the nitrogen concentration of the tracheal sap, but not the content of xylem nitrogen per volume of stem material. The orientation of the stems in the tree and the diameter of the stems had an effect on their contents of xylem nitrogen, with southeastern orientation and thinner stems showing higher concentrations.We could not detect the presence of ammonium, nitrites or proteins in the tracheal sap of orange trees. Most of the nitrogen was present as amino acids and about 2% of the total in the form of nitrates. The qualitative composition of amino acids, as determined by TLC, was the same both in winter and spring tracheal sap. The main components of the sap were proline and arginine in winter, and these amino acids together with asparagine and aspartic acid in spring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1980.tb04466.x
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  • 4
    Electronic Resource
    Electronic Resource
    Proteolysis of ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of Citrus explants throughout the annual cycle and its regulation by ethylene (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 73 (1988), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Leaf senescence and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) degradation in orange [Citrus sinensis (L.) Osbeck cv. Washington Navel] explants have been investigated. Explants consisted of a segment of stem (ca 15 cm) and 5 mature leaves. In vitro RuBP carboxylase degradation was determined by culturing the explants in water for different periods of time (3 days usually) and quantifying the two RuBP carboxylase subunits in the extracts following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In vitro RuBP carboxylase degradation was estimated by autodigestion of leaf extracts and SDS-PAGE. The extent of in vivo RuBP carboxylase degradation in explants cultured under 16 h light/8 h dark photoperiod varied throughout the year and showed a cyclic behaviour correlated with the growth cycle of Citrus. The highest proteolytic activity both in vivo and in vitro was found in explants made from April to August coinciding with the maximum vegetative growth period of the tree.Leaf senescence and abscission could be retarded significantly at any time of the year by maintaining the explants continuously in the dark. Treatment of the explants in the dark with a continuous flow of ethylene enhanced both leaf abscission and rate of RuBP carboxylase degradation, proportionally to ethylene concentration (0.1-0.6 ppm). Ethylene-induced senescence of Citrus leaf explants in the dark appears to be a convenient model system to study the regulation of the proteolytic degradation of RuBP carboxylase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb09184.x
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  • 5
    Electronic Resource
    Electronic Resource
    Seasonal variation of nitrogenous compounds in the xylem sap of Citrus (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 59 (1983), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Samples of tracheal sap of Citrus sinensis (L.) Osbeck cv. Washington Navel were taken from field trees throughout the year and the nitrogen composition of the sap was determined. The nitrogenous fraction of the sap was composed mainly of free amino acids (92–97% of total nitrogen) and nitrates throughout the year. Proline was the most abundant amino acid during almost the entire cycle, and its concentration was especially high during the autumn and winter period. Nevertheless, a significant part (40–60%) of the total organic nitrogen was transported as arginine. Total nitrogen as well as amino acids and nitrates were maximal at spring flush. At spring flush and summer flush there was also a diversification of α-amino nitrogen among different amino acids. During the spring flush, nitrates, asparagine and γ-aminobutyric acid in the xylem sap seemed to have a radicular origin, whereas glutamic acid and arginine were released from the surrounding parenchyma. The results suggest a metabolic transformation in the wood parenchyma of nitrogenous compounds coming from the roots (including reduction of nitrates) and a turnover of different nitrogen metabolites between the xylem and surrounding cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1983.tb06298.x
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  • 6
    Electronic Resource
    Electronic Resource
    Nitrogen accumulation and mobilization in Citrus leaves throughout the annual cycle (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 61 (1984), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The changes of protein and amino acid contents of young and old leaves from field citrus trees [Citrus sinensis (L.) Osbeck cv. Washington Navel] were studied throughout the year. the total protein content of old leaves decreased during the spring and summer growths, whereas in young developing leaves it increased rapidly. The end of the spring and summer flushes was followed by a quick recovery of the initial protein content due to a process of reversible senescence. The evolution of SDS-PAGE proteinograms indicated that most of the foliar proteins contributed to the nitrogen mobilization during the spring and summer growth periods. A protein band of molecular weight ca 55,000, probably containing the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, decreased relatively more than the others. The amino acid content of the leaves increased during winter time due to the accumulation of proline, which was mobilized during the spring flush. The possible nitrogen storage function of proline is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1984.tb06351.x
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  • 7
    Electronic Resource
    Electronic Resource
    An experimental assessment of the Wagner-Sedman extraction theory for the intestinal absorption of antibacterial sulfonamides (1980)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 8 (1980), S. 297-309 
    Details
    ISSN: 1573-8744
    Keywords: Sulfonamides ; absorption rate constants ; reverse-phase partition chromatography ; Wagner-Sedman extraction theory ; absorption from the small intestine ; logarithmiclogistic correlations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The chromatographic parameters in a reverse-phase partition system and the rat gut in situabsorption rate constants for 18 antibacterial sulfonamides are highly correlated values. The correlation is logarithmic-logistic in nature, being in accordance with the Wagner-Sedman extraction theory for a constant pH value. Parabolic correlations did not satisfactorily fit the experimental data. This behavior, not frequently reported in regard to the intestinal absorption of drugs, is discussed in connection with other apparently contradictory available data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01059647
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  • 8
    Electronic Resource
    Electronic Resource
    Intestinal absorption-partition relationships: A tentative functional nonlinear model (1981)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 9 (1981), S. 191-215 
    Details
    ISSN: 1573-8744
    Keywords: intestinal absorption ; absorption models ; Wagner-Sedman extraction theory ; absorption-partition relationships ; parabolic correlations ; bilinear correlations ; hyperbolic logarithmic-logistic correlations ; pore diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Models and equations designed to elucidate passive intestinal absorption mechanisms by analysis of the relationship between the absorption rate constant (ka)and either the partition coefficients (P)or a related partition constant for homologous series of substances, are reviewed. Classical nonlinear physical models, such as those which assume the existence of a nonstirred layer or equilibrium extraction, predict sigmoidal or hyperbolic relationships between ka and P,whereas other models, which regard the membrane as a heterogeneous multicompartment system, predict parabolic or bilinear relationships between log ka and log P.In the present paper, an alternative model is proposed, which incorporates the Wagner-Sedman equilibrium extraction model together with the existence of pores, which play a fundamental role for compounds below 250in molecular weight. Several apparently contradictory absorption-partition literature data are shown to be highly consistent with the tentative model proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01068082
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  • 9
    Electronic Resource
    Electronic Resource
    Oxidative modification and breakdown of ribulose-1,5-bisphosphate carboxylase/oxygenase induced in Euglena gracitis by nitrogen starvation (1994)
    Springer
    Planta 193 (1994), S. 208-215 
    Details
    ISSN: 1432-2048
    Keywords: Chloroplast senescence ; Euglena ; Nitrogen storage ; Proteolysis ; Ribulose-1,5-bisphosphate carboxylase/oxygenase (oxidative modification)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When photoheterotrophic Euglena gracilis Z Pringsheim was subjected to nitrogen (N)-deprivation, the abundant photosynthetic enzyme ribulose-1,5-bis-phosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) was rapidly and selectively degraded. The breakdown began after a 4-h lag period and continued for a further 8 h at a steady rate. After 12 h of starvation, when the amount of Rubisco was reduced to 40%, the proteolysis of this enzyme slowed down while degradation of other proteins started at a similar pace. This resulted in a decline of culture growth, chloroplast disassembly — as witnessed by chlorophyll (Chl) loss — and cell bleaching. Experiments with spectinomycin, an inhibitor of chloroplastic translation, indicated that there was an absolute increase in the rate of Rubisco degradation in the N-deprived culture as compared with control conditions, where no significant carboxylase breakdown was detected. Oxidative aggregation of Rubisco (as detected by non-reductive electrophoresis) and association of the enzyme to membranes increased with time of N-starvation. Fluorescent labeling of oxidized cysteine (Cys) residues with monobromobimane indicated a progressive oxidation of Cys throughout the first hours of N-deprivation. It is concluded that Rubisco acts as an N store in Euglena, being first oxidized, and then degraded, during N-starvation. The mobilization of Rubisco allows sustained cell growth and division, at almost the same rate as the control (non-starved) culture, during 12 h of N-deprivation. Afterwards, breakdown is extended to other photosynthetic structures and the whole chloroplast is dismantled while cell growth is greatly reduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192532
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  • 10
    Electronic Resource
    Electronic Resource
    Redox regulation of enzymatic activity and proteolytic susceptibility of ribulose-1,5-bisphosphate carboxylase/oxygenase fromEuglena gracilis (1993)
    Springer
    Photosynthesis research 35 (1993), S. 55-66 
    Details
    ISSN: 1573-5079
    Keywords: cysteine oxidation ; Euglena gracilis ; protein turnover ; proteolytic susceptibilization ; ribulose-1,5-bisphosphate carboxylase/oxygenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase fromEuglena gracilis decays steadily when exposed to agents that induce oxidative modification of cysteine residues (Cu2+, benzofuroxan, disulfides, arsenite, oxidized ascorbate). Inactivation takes place with a concomitant loss of cysteine sulfhydryl groups and dimerization of large subunits of the enzyme. 40% activity loss induced by the vicinal thiol-reagent arsenite is caused by modification of a few neighbor residues while the almost complete inactivation achieved with disulfides is due to extensive oxidation leading to formation of mixed disulfides with critical cysteines of the protein. In most cases oxidative inactivation is also accompanied by an increased sensitivity to proteolysis by trypsin, chymotrypsin or proteinase K. Both enzymatic activity and resistance to proteolysis can be restored through treatment with several thiols (cysteamine, cysteine, dithiothreitol and, more slowly, reduced glutathione). Redox effectors which are thought to regulate the chloroplast activity (NADPH, ferredoxin and thioredoxin) do not reactivate the oxidized enzyme. When ribulose-1,5-bisphoshate carboxylase/oxygenase is incubated with cystamine/cysteamine mixtures having different disulfide/thiol ratio (r), inactivation takes place around r=1.5 while proteolytic sensitization occurs under more oxidative conditions (r=4). It is suggested that oxidative modification may happen in vivo under exceptional circumstances, such as senescence, bleaching or different kinds of stress, leading to enzyme inactivation and triggering the selective degradation of the carboxylase that has been repeatedly observed during these processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185411
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