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  • 1
    Electronic Resource
    Electronic Resource
    Evidence for two Types of Mediation of Neutral Amino-Acid Transport in Ehrlich Cells (1963)
    [s.l.] : Nature Publishing Group
    Nature 197 (1963), S. 765-767 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] BECAUSE many of the neutral amino-acids compete with one another for transport1-, at least in mammalian systems, a common mediation has generally been taken to serve for them all. A lack of strict quantitative agreement between the affinities indicated by initial rates, and those indicated by ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/197765a0
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  • 2
    Electronic Resource
    Electronic Resource
    Transport of Gabapentin, a γ-Amino Acid Drug, by System L α-Amino Acid Transporters: A Comparative Study in Astrocytes, Synaptosomes, and CHO Cells (1995)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 64 (1995), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The system L transporter is generally considered to be one of the major Na+-independent carriers for large neutral α-amino acids in mammalian cells. However, we found that cultured astrocytes from rat brain cortex accumulate gabapentin, a γ-amino acid, predominantly by this α-amino acid transport system. Uptake of gabapentin by system L transporter was also examined in synaptosomes and Chinese hamster ovary (CHO) cells. The inhibition pattern displayed by various amino acids on gabapentin uptake in astrocytes and synaptosomes corresponds closely to that observed for the system L transport activity in CHO cells. Gabapentin and leucine have Km values that equal their Ki values for inhibition of each other, suggesting that leucine and gabapentin compete for the same system L transporter. By contrast, gabapentin exhibited no effect on uptake of GABA, glutamate, and arginine, indicating that these latter three types of brain transporters do not serve for uptake of gabapentin. A comparison of computer modeling analysis of gabapentin and l-leucine structures shows that although the former is a γ-amino acid, it can assume a conformation that can resemble the L-form of a large neutral α-amino acid such as l-leucine. The steady-state kinetic study in astrocytes and CHO cells indicates that the intracellular concentrations of gabapentin are about two to four times higher than that of leucine. The uptake levels of these two substrates are inversely related to their relative exodus rates. The concentrating ability by system L observed in astrocytes is consistent with the substantially high accumulation gradient of gabapentin in the brain tissue as determined by microdialysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1995.64052125.x
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  • 3
    Electronic Resource
    Electronic Resource
    BINDING PROTEINS AND MEMBRANE TRANSPORT (1975)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 264 (1975), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1975.tb31496.x
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  • 4
    Electronic Resource
    Electronic Resource
    Regulation and Genetics of Amino Acid Transport (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 456 (1985), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1985.tb14892.x
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  • 5
    Electronic Resource
    Electronic Resource
    Gene Transfer and Cloning of the Amino-Acid Transport System L from Human Cells (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 456 (1985), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1985.tb14893.x
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  • 6
    Electronic Resource
    Electronic Resource
    A Chinese hamster ovary leucyl-tRNA synthetase mutant with a uniquely altered high molecular weight leucyl-tRNA synthetase complex (1984)
    Springer
    Biochemical genetics 22 (1984), S. 349-355 
    Details
    ISSN: 1573-4927
    Keywords: leucyl-tRNA ; Chinese hamster ovary enzyme complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The Chinese hamster ovary (CHO) cell culture temperature-sensitive mutant ts025Cl with a defect in leucyl-tRNA synthetase (LeuRS) does not have an inherently more thermolabile LeuRS, but instead the mutation causes the complete loss of the LeuRS high molecular weight complexes which are present in normal wild-type cells. The mutant cell LeuRS has a single 8 S enzyme form which corresponds hydrodynamically to the 8 S free form of wild-type enzyme. Both 8 S forms have the same thermostability and the same K m for leucine, indicating that there is no inherent defect in the catalytic activity of the enzyme. The temperature-sensitive phenotype can be explained by the lack of thermostable high molecular weight forms of LeuRS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00484233
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  • 7
    Electronic Resource
    Electronic Resource
    Cloning, expression, and nucleotide sequence of livR, the repressor for high-affinity branched-chain amino acid transport in Escherichia coli (1986)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 1 (1986), S. 125-133 
    Details
    ISSN: 0887-3585
    Keywords: regulation ; prokaryotic bacteria ; leucine uptake ; leucyl tRNA corepressor ; cell physiology ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The livR gene encoding the repressor for high-affinity branched-chain amino acid transport in Escherichia coli has been cloned from a library prepared from the episome F106. The inserted DNA fragment from the initial cloned plasmid, pANT1, complemented two independent, spontaneously derived, regulatory mutations. Subcloning as well as the creation of deletions with Bal31 exonuclease revealed that the entire regulatory region is contained within a 1.1-kb RsaI-SalI fragment. Expression of the pANT plasmids in E. coli minicells showed that the regulatory region encodes one detectable protein with an apparent molecular weight of 21,000. DNA sequencing revealed one open reading frame of 501 bp encoding a protein with a calculated MW of 19,155. The potential secondary structure of the regulatory protein has been predicted and it suggests that the carboxy terminus may fold into three consecutive alpha helices. These results suggests that the livR gene encodes a repressor which plays a role in the regulation of expression of the livJ and the livK transport genes.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340010204
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  • 8
    Electronic Resource
    Electronic Resource
    Formation of heterodimers between wild type and mutant trp aporepressor polypeptides of Escherichia coli (1988)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 4 (1988), S. 173-181 
    Details
    ISSN: 0887-3585
    Keywords: DNA binding protein ; ligand binding ; equilibrium dialysis ; dimer ; stability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Availability of the three-dimensional structure of the trp repressor of Escherichia coli and a large group of repressor mutants has permitted the identification and analysis of mutants with substitutions of the amino acid residues that from the tryptophan binding pocket. Mutant aporepressors selected for study were overproduced using a multicopy expression plasmid. Equilibrium dialysis with 14C-tryptophan and purified mutant and wild type aporepressors was employed to determine tryptophan binding constants. The results obtained indicate that replacement of theronine 44 by methionine (TM44) or arginine 84 by histidine (RH84) lowers the affinity for tryptophan approximately two-and four-fold, respectively. Replacement of ariginine 54 by histidine (RH84) or glycine 85 by ariginine (GR85) results in complete loss of tryptophan binding activity. Purified mutant and wild type aporepressors were used in vitro heterodimer studies. The trp repressor of E. coli functions as a stable dimer. A large number of trp repressor mutants prduces defective repressors that are transdominant to the wild type repressor in vivo. The transdominance presumably results from the formation of inactive or slightly active heterodimers between the mutant and wild type polypeptide subunits. An in vitro assay was developed to detect and measure heterodimer formation. Heterodimer formation was thermally induced, and heterodimers were separated on nondenaturing polyacrylamide gels. Aporepressors readily formed heterodimer formation upon treatment at 65°C for 3 minutes. Heterodimer formation was significantly retarded by the presence of the corepressor, L-tryptophan. Indole-3-propionic acid, 5-methyl tryptophan, and other analogs of tryptophan, as well as indole, also inhibited heterodimer formation. These results indicate that the presence of the indole moiety in the corepressor binding pocket increases the stability of the dimer.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340040304
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  • 9
    Electronic Resource
    Electronic Resource
    Carbon-starvation induction of the ugp operon, encoding the binding protein-dependent sn-glycerol-3-phosphate transport system in Escherichia coli (1991)
    Springer
    Molecular genetics and genomics 230 (1991), S. 28-32 
    Details
    ISSN: 1617-4623
    Keywords: ugp operon, gene regulation ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gene products of the ugp operon of Escherichia coli are responsible for the uptake of sn-glycerol-3-phosphate and certain glycerophosphodiesters. The regulation of ugp is mainly phoBR-dependent. Significant expression, however, can be observed even in the presence of high concentrations of phosphate, a condition which normally completely represses pho expression. Pho-independent ugp expression was found to be derepressed during the late logarithmic growth phase due to carbon starvation. Among different carbon sources tested, glucose caused the most complete repression. Addition of cAMP prevented glucose repression, indicating that a cAMP-CRP control mechanism may be directly or indirectly involved in the carbon-starvation response. This conclusion is supported by the fact that pho-independent ugp expression correlated with the presence of the cya and crp gene products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00290646
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  • 10
    Electronic Resource
    Electronic Resource
    Transport of amino acids in intact 3T3 and SV3T3 cells. Binding activity for leucine in membrane preparations of ehrlich ascites tumor cells (1976)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 4 (1976), S. 441-447 
    Details
    ISSN: 0091-7419
    Keywords: Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Transport of amino acids into 3T3 and SV3T3 (SV40 virus-transformed 3T3) cells was measured on glass cover slips. The 3T3 and SV3T3 cells contain both A (alanine preferring) and L (leucine preferring) systems for neutral amino acid transport. Initial rates of uptake of amino acids are about twofold higher in SV3T3 than in 3T3 cells. Other parameters measured, however, do not indicate marked differences in the transport of amino acids by the two cell types. L-system amino acids, such as leucine, are subject to trans-stimulation in both cell lines, whereas A-system amino acids, such as alanine and glycine, are not. Leucine was transported to higher levels in confluent cells than in nonconfluent cells. Glycine, however, shows distinctly less transport activity as the cells become confluent.Ehrlich ascites cell plasma membranes were prepared and assayed for amino acid-binding activity. Leucine-binding activity was detected by equilibrium dialysis in Triton X-100-treated membrane preparations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400040403
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