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  • 1
    Electronic Resource
    Electronic Resource
    Transport of glutamine inXenopus laevis oocytes: Relationship with transport of other amino acids (1989)
    Springer
    The journal of membrane biology 112 (1989), S. 149-157 
    Details
    ISSN: 1432-1424
    Keywords: Xenopus oocyte ; amino acid ; Na+-dependent transport ; glutamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have investigated transport of the amino acid glutamine across the surface membranes of prophase-arrestedXenopus laevis oocytes. Glutamine accumulation was linear with time for 30 min; it was stereospecific with aK m of 0.12±0.02mm andV max of 0.92±0.17 pmol/oocyte · min forl-glutamine. Transport ofl-glutamine was Na+-dependent, the cation not being replaceable with Li+, K+, choline, tris(hydroxymethyl)-aminomethane (Tris), tetramethylammonium (TMA) or N-methyld-glucamine NMDG); external Cl− appeared to be necessary for full activation of Na+-dependent glutamine transport. Two external Na+ may be required for the transport of one glutamine molecule.l-glutamine transport (at 50 μm glutamine) was inhibited by the presence of other amino acids:l-alanine,d-alanine,l-leucine,l-asparagine andl-arginine (about 60% inhibition at 1mm);l-histidine,l-valine and glycine (25 to 40% inhibition at 1mm);l-serine,l-lysine,l-phenylalanine andl-glutamate (45 to 55% inhibition at 10mm). N-methylaminoisobutyric acid (meAIB) had no effect at 10mm, but 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) inhibited Na+/glutamine transport by about 50% at 10mm.l-glutamine was a competitive inhibitor of the Na+-dependent transport ofl-alanine,d-alanine andl-arginine; this evidence is consistent with the existence of a single system transporting all four amino acids. Glutamine uptake in oocytes appears to be catalyzed by a transport system distinct from the cotransport Systems A, ASC, N and Gly, although it resembles System B0,+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871276
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  • 2
    Electronic Resource
    Electronic Resource
    Transport and membrane binding of the glutamine analogue 6-diazo-5-oxo-L-norleucine (DON) in Xenopus laevis oocytes (1992)
    Springer
    The journal of membrane biology 128 (1992), S. 181-191 
    Details
    ISSN: 1432-1424
    Keywords: Xenopus oocyte ; amino acid ; Na+-dependent transport ; membrane binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have examined transport and membrane binding of 6-diazo-5-oxo-l-norleucine (DON, a photoactive diazo-analogue of glutamine) and their relationships to glutamine transport in Xenopus laevis oocytes. DON uptake was stereospecific and saturable (V max of 0.44 pmol/oocyte · min and a K m of 0.065 mm). DON uptake was largely Nau+ dependent (80% at 50 μ m DON) and inhibited (〉75%) by glutamine and arginine (substrates of the System B0,+ transporter) at 1 mm. Glutamine and DON show mutual competitive inhibition of Na+-dependent transport. Preincubation of oocytes in medium containing 0.1 mm DON for 24 or 48 hr depressed the V max for System B0,+ transport (as measured by Na+-dependent glutamine uptake), this effect was highly specific (neither d-DON nor the System B0,+ substrates glutamine and d-alanine showed any independent effect) and required Na+ ions. Glutamine (1 mm in preincubation medium) protected transport from inhibition by DON. The possibility that specific inactivation of System B0,+ by DON reflects attachment of DON to the transporter was tested by examining the binding of [14C]DON to Xenopus oocyte membranes. Oocytes incubated in 100 mm NaCl in the presence of [14C]DON for up to 48 hr showed 2.4-fold higher 14C-binding to membranes than oocytes incubated in choline chloride. Na+-dependent DON binding (31 ± 11 fmol/μg membrane protein) was suppressed by external glutamine, arginine or alanine and was largely confined to a membrane protein fraction of 48–65 kDa (as assessed by SDS-polyacrylamide gel electrophoresis). The present studies indicate that DON and glutamine uptake in oocytes are both mediated by System B0,+ and demonstrate that DON binding to a particular membrane protein fraction is associated with inactivation of the transporter, offering the prospect of using [14C]DON as a covalent label for the transport protein in order to facilitate its isolation and subsequent biochemical characterization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231811
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  • 3
    Electronic Resource
    Electronic Resource
    Control of the Size of the Human Muscle Mass (2004)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 66 (2004), S. 799-828 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: This review is divided into two parts, the first dealing with the cell and molecular biology of muscle in terms of growth and wasting and the second being an account of current knowledge of physiological mechanisms involved in the alteration of size of the human muscle mass. Wherever possible, attempts have been made to interrelate the information in each part and to provide the most likely explanation for phenomena that are currently only partially understood. The review should be of interest to cell and molecular biologists who know little of human muscle physiology and to physicians, physiotherapists, and kinesiologists who may be familiar with the gross behavior of human muscle but wish to understand more about the underlying mechanisms of change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physiol.66.052102.134444
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  • 4
    Electronic Resource
    Electronic Resource
    Control of the Size of the Human Muscle Mass (2004)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 66 (2004), S. 799-828 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: This review is divided into two parts, the first dealing with the cell and molecular biology of muscle in terms of growth and wasting and the second being an account of current knowledge of physiological mechanisms involved in the alteration of size of the human muscle mass. Wherever possible, attempts have been made to interrelate the information in each part and to provide the most likely explanation for phenomena that are currently only partially understood. The review should be of interest to cell and molecular biologists who know little of human muscle physiology and to physicians, physiotherapists, and kinesiologists who may be familiar with the gross behavior of human muscle but wish to understand more about the underlying mechanisms of change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physiol.66.052102.134444
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  • 5
    Electronic Resource
    Electronic Resource
    PROTEIN AND AMINO ACID METABOLISM DURING AND AFTER EXERCISE AND THE EFFECTS OF NUTRITION (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Nutrition 20 (2000), S. 457-483 
    Details
    ISSN: 0199-9885
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Sustained dynamic exercise stimulates amino acid oxidation, chiefly of the branched-chain amino acids, and ammonia production in proportion to exercise intensity; if the exercise is intense enough, there is a net loss of muscle protein (as a result of decreased protein synthesis, increased breakdown, or both); some of the amino acids are oxidized as fuel, whereas the rest provide substrates for gluconeogenesis and possibly for acid-based regulation. Protein balance is restored after exercise, but no hypertrophy occurs with habitual dynamic exercise. Resistance exercise causes little change in amino acid oxidation but probably depresses protein synthesis and elevates breakdown acutely. After exercise, protein synthesis rebounds for 〈=48 h, but breakdown remains elevated, and net positive balance is achieved only if amino acid availability is increased. There is no evidence that habitual exercise increases protein requirements; indeed protein metabolism may become more efficient as a result of training.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.nutr.20.1.457
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  • 6
    Electronic Resource
    Electronic Resource
    Different patterns of protein turnover in skeletal and gastrointestinal smooth muscle and the production of Nτ-methylhistidine during fasting in the rat (1986)
    Springer
    Bioscience reports 6 (1986), S. 143-153 
    Details
    ISSN: 1573-4935
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract During four days of fasting in rats skeletal muscle protein synthesis fell pro-gressively, whereas skeletal muscle protein breakdown was unchanged until the third and fourth days when it rose dramatically. In contrast, the synthetic rate of smooth muscle protein was unchanged during three days of fasting despite a loss of protein content, indicating an abrupt rise in protein breakdown in this tissue on the first day of fasting which was sustained thereafter. Urinary excretion of Nτ-methylhistidine was significantly increased throughout fasting. The concentration of free Nτ-methylhistidine in plasma and in muscle tissue was elevated throughout the period of fasting. This elevation was not caused by reduced renal clearance, but appears to have been mainly the result of increased breakdown of Nτ-methylhistidine-containing proteins in tissues other than skeletal muscle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01115000
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  • 7
    Electronic Resource
    Electronic Resource
    Preparation of CO2 from blood and protein-bound amino acid carboxyl groups for quantification and 13C-isotope measurements (1984)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 11 (1984), S. 348-352 
    Details
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements of protein and amino acid metabolism in man using stable isotopes and selected ion monitoring gas chromatographic/mass spectrometric techniques are limited by the requirement of relatively high levels of labelling for adequate precision ( 〉 0.05 at % excess). We describe here a means of extending the scope of such studies by measurement of lower levels of enrichment achieved in gaseous CO2 derived from whole blood or protein-bound amino acids following the administration of tracer amounts of appropriately labelled substrates. Construction and operation of a novel glass vacuum line required for this work are described in detail and specific applications relevant to clinical investigations are outlined. Measurements of both the total amount of CO2 and its 13C enrichment are performed in an isotope-ratio mass spectrometer which provides acceptable levels of accuracy and reproducibility for both measurements ( ±0.1% and ±0.0001 at% excess respectively).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200110706
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  • 8
    Electronic Resource
    Electronic Resource
    Automated measurement of 13C enrichment in carbon dioxide derived from submicromole quantities of L-(1-13C)-leucine (1988)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 15 (1988), S. 369-374 
    Details
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C enrichment of the carboxyl carbon of leucine was measured by isotope ratio mass spectrometry after conversion to CO2 by reaction with ninhydrin in a Vacutainer and cryogenic purification using the Finnigan MAT Breath Gas Analysis System designed for processing 13C breath test samples. The sources of error which arise with submicromole samples are examined and corrections provided for suboptimal mass spectrometer signals and contamination of the evolved CO2 with CO2 from the reaction medium. The main limitations to the accuracy and precision of the method are not instrumental but arise from the contamination with residual CO2 in the reaction medium, and this sets a lower limit of around 0.25 μmol leucine on the practical sample size. This is an improvement of about five-fold on the previous manual method of CO2 isolation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200150704
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  • 9
    Electronic Resource
    Electronic Resource
    Automated measurement of the concentration and 13C enrichment of carbon dioxide in breath and blood samples using the finnigan MAT breath gas analysis system (1988)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 15 (1988), S. 365-367 
    Details
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The operation and performance of the Finnigan MAT automated Breath Gas Analysis System for the routine analysis of 13C breath tests taken in 20-ml Vacutainers is described. Up to four samples per hour can be analysed with a standard deviation of δ13C of 〈0.05%o being achieved over the range 10-50 μmol CO2. The equipment can also be used for the automatic measurement of the concentration and 13C enrichment of CO2 derived from carbonate or bicarbonate solutions, including blood and other physiological fluids.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200150703
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  • 10
    Electronic Resource
    Electronic Resource
    Measurement of muscle protein fractional synthetic rate by capillary gas chromatography/combustion isotope ratio mass spectrometry (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1992), S. 486-490 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The measurement of skeletal muscle protein fractional synthetic rate using an infusion of (1-13C)leucine and measuring the isotopic abundance of the tracer in skeletal muscle protein by preparative gas chromatography (GC)/ninhydrin isotope ratio mass spectrometry (IRMS) is laborious and subject to errors owing to contamination by 12C. The purpose of this study was to compare muscle (13C)leucine enrichment measured with the conventional preparative GC/ninhydrin IRMS approach to a new, continuous-flow technique using capillary GC/combustion IRMS. Quadriceps muscles were removed from four Sprague-Dawley rats after each was infused at a different rate with (1-13C)leucine for 6-8 h. Muscle leucine enrichment (at.% excess) measured by both methods differed by less than 4%, except at low (13C)leucine enrichments (〈0.03 at.% excess). In addition, capillary GC/combustion IRMS was used to assess muscle (13C)leucine enrichment and fractional muscle protein synthesis rate in ten normal young men and women infused with (1,2-13C2)leucine for 12-14 h. This approach reduced the variability of the isotope abundance measure and gave estimates of muscle protein synthesis rate (0.050 ± 0.011% h-1 (mean ± SEM); range = 0.023-0.147% h-1) that agree with published values determined using the standard analytical approach. The measurement of (13C)leucine enrichment from skeletal muscle protein by capillary GC/combustion IRMS provides a simple, acceptable and practical alternative to preparative GC/ninhydrin IRMS.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200211004
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