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  • 1
    Electronic Resource
    Electronic Resource
    Activation potassium efflux from Escherichia coli by glutathione metabolites (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The mechanism by which N-ethylmaleimide (NEM) elicits potassium efflux from Escherichia coli has been investigated. The critical factor is the formation of specific glutathione metabolites that activate transport systems encoded by the kefB and kefC gene products. Formation of N-ethyl-succinimido-S-glutathione (ESG) leads to the activation of potassium efflux via these transport systems. The addition of dithiothreitol and other reducing agents to cells reverses this process by causing the breakdown of ESG and thus removing the activator of the systems. Chlorodinitrobenzene, p-chloromercuribenzoate and phenylmaleimide provoke similar effects to NEM. Iodoacetate, which leads to the formation of S-carboxymethyl-glutathione, does not activate the systems but does prevent the action of NEM. It is concluded that the KefB and KefC systems are gated by glutathione metabolites and that the degree to which they are activated is dependent upon the nature of the substituent on the sulphydryl group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1990.tb00607.x
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  • 2
    Electronic Resource
    Electronic Resource
    The cloning and DNA sequence of the gene for the glutathione-regulated potassium-efflux system KefC of Escherichia coli (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The kefC gene of Escherichia coli encodes a potassium-efflux system that is regulated by glutathione metabolites. The close proximity of the E. coli kefC gene to the folA gene, encoding dihydrofolate reductase, has been utilized to clone the structural gene for the system from a Clarke-Carbon plasmid. The cloned gene has been refined to a region of DNA approximately 2.1 kb in length using exonuclease III-generated deletions and random Muc/M1734 (IacZ) insertions. The direction of transcription has been deduced from the orientation of the Mu insertions in the cloned DNA. A hybrid protein consisting of approximately two thirds of the KefC protein fused to β-galactosidase has been shown to be membrane-located. The DNA sequence of the gene has been determined and an open reading frame of 1.86kb has been located which could encode a protein of 620 amino acids (7901 0Da). Using the T7 expression system a membrane protein, of apparent molecular mass 55–60 kDa, has been shown to be encoded by the kefC gene. The predicted protein sequence shows a highly hydrophobic amino-terminus and a strongly hydrophilic carboxy-terminus, Comparison of the amino acid sequence of the kefC gene product with those of two glutathione-utilizing enzymes, glyoxalase and dehalogenase, has revealed some similarities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb00731.x
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  • 3
    Electronic Resource
    Electronic Resource
    Phosphorus retention and release from sandy soils of the Peel-Harvey catchment (1993)
    Springer
    Nutrient cycling in agroecosystems 36 (1993), S. 115-122 
    Details
    ISSN: 1573-0867
    Keywords: phosphorus ; retention ; release ; sandy soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In order to manage phosphorus (P) losses from soils to waterbodies, knowledge of the mechanisms through which P is retained or released from the soil is essential. Sandy soils of the Peel-Harvey catchment (Western Australia) were subjected to a range of environmental and management factors in the laboratory and field in order to gain an understanding of the mechanisms that affect the magnitude of P losses. Sandy soils accumulated P, despite having little sorption capacity, and this accumulation could be monitored by measuring an acid-extractable fraction. The potential, short-term P loss could be estimated by determination of water-soluble soil solution P prior to winter rains. An annual cycle of the change in arbitrarily defined soil-P pools is discussed in relation to environmental and management factors. Laboratory experiments indicated that P rundown and potential annual P loss in the absence of P fertilizers could be estimated using bicarbonate extractable P. Phosphorus losses were decreased by the application of fertilizers with a low content of water-soluble P. The low ability of sandy soils of the Peel-Harvey coastal catchment to retain P, when compared to other Western Australian soils, is because of low contents of clay minerals and iron and aluminium hydrous oxides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00747581
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  • 4
    Electronic Resource
    Electronic Resource
    A comparison of soil tests to predict the growth and nodulation of subterranean clover in aluminium-toxic topsoils (1991)
    Springer
    Plant and soil 136 (1991), S. 11-24 
    Details
    ISSN: 1573-5036
    Keywords: aluminium toxicity ; 8-hydroxyquinoline ; cation exchange resin ; reactive Al ; soil test ; soil solution ; 1∶5 extract ; acidic topsoil ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Total Al concentration or pH in 1∶5 10 mM CaCl2 extracts and exchangeable Al in 100 mM BaCl2 extracts cannot always distinguish between Al-toxic and Al-nontoxic topsoils. Our objectives were to compare the abilities of different measures of Al and pH in various extracts to predict the effects of acidity on growth and nodulation of subterranean clover. In a glasshouse experiment,Trifolium subterraneum L. cv. Mt Barker was grown in acidic soils from 3 sites in the Western Australian wheatbelt with different histories of phosphate fertilizer application. The pH was adjusted to give a range of 3.8–7 in the centrifuged soil solution (SS). Total (Al-tot), reactive Al (8-hydroxyquinoline-extractable, Al-HQ) and pH were measured in SS and 1∶5 extracts of KCl, CaCl2 and LaCl3. Another method of estimating reactive Al (Al which reacts with Chelex-100) was also measured in SS only. Other measurements included exchangeable Al and H, Ca in SS, and P in SS and the CaCl2 extracts. Both plant growth and early nodulation decreased with increasing acidity. Plant growth in the acidified and unlimed treatments of all soils was best described by Al-HQ in SS, KCl or CaCl2 (r2=0.68–0.70). Multiple regression of relative yield against Al or pH with the concentration of P in SS increased the percentage variation explained by 10% and 30%, respectively. Early nodulation was well correlated (r2=0.67–0.91) with pH or exch. H, Al-tot or exch. Al and Al-HQ. No improvement in the correlation was gained by including P using multiple regression. At constant ionic strength, increasing the valence of the extracting cation decreased the ability of soil tests to distinguish phytotoxic Al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02465215
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