Journal articles: 'Isotopic label'

1

Seeger, Stefan, and Markus Weiler. "Temporal dynamics of tree xylem water isotopes: in situ monitoring and modeling." Biogeosciences 18, no. 15 (August 12, 2021): 4603–27. http://dx.doi.org/10.5194/bg-18-4603-2021.

Full text

Abstract:

Abstract. We developed a setup for a fully automated, high-frequency in situ monitoring system of the stable water isotope deuterium and 18O in soil water and tree xylem. The setup was tested for 12 weeks within an isotopic labeling experiment during a large artificial sprinkling experiment including three mature European beech (Fagus sylvatica) trees. Our setup allowed for one measurement every 12–20 min, enabling us to obtain about seven measurements per day for each of our 15 in situ probes in the soil and tree xylem. While the labeling induced an abrupt step pulse in the soil water isotopic signature, it took 7 to 10 d until the isotopic signatures at the trees' stem bases reached their peak label concentrations and it took about 14 d until the isotopic signatures at 8 m stem height leveled off around the same values. During the experiment, we observed the effects of several rain events and dry periods on the xylem water isotopic signatures, which fluctuated between the measured isotopic signatures observed in the upper and lower soil horizons. In order to explain our observations, we combined an already existing root water uptake (RWU) model with a newly developed approach to simulate the propagation of isotopic signatures from the root tips to the stem base and further up along the stem. The key to a proper simulation of the observed short-term dynamics of xylem water isotopes was accounting for sap flow velocities and the flow path length distribution within the root and stem xylem. Our modeling framework allowed us to identify parameter values that relate to root depth, horizontal root distribution and wilting point. The insights gained from this study can help to improve the representation of stable water isotopes in trees within ecohydrological models and the prediction of transit time distribution and water age of transpiration fluxes.

APA, Harvard, Vancouver, ISO, and other styles

2

Miller, Benjamin F., Christopher A. Wolff, Fredrick F. Peelor, Patrick D. Shipman, and Karyn L. Hamilton. "Modeling the contribution of individual proteins to mixed skeletal muscle protein synthetic rates over increasing periods of label incorporation." Journal of Applied Physiology 118, no. 6 (March 15, 2015): 655–61. http://dx.doi.org/10.1152/japplphysiol.00987.2014.

Full text

Abstract:

Advances in stable isotope approaches, primarily the use of deuterium oxide (2H2O), allow for long-term measurements of protein synthesis, as well as the contribution of individual proteins to tissue measured protein synthesis rates. Here, we determined the influence of individual protein synthetic rates, individual protein content, and time of isotopic labeling on the measured synthesis rate of skeletal muscle proteins. To this end, we developed a mathematical model, applied the model to an established data set collected in vivo, and, to experimentally test the impact of different isotopic labeling periods, used 2H2O to measure protein synthesis in cultured myotubes over periods of 2, 4, and 7 days. We first demonstrated the influence of both relative protein content and individual protein synthesis rates on measured synthesis rates over time. When expanded to include 286 individual proteins, the model closely approximated protein synthetic rates measured in vivo. The model revealed a 29% difference in measured synthesis rates from the slowest period of measurement (20 min) to the longest period of measurement (6 wk). In support of these findings, culturing of C2C12 myotubes with isotopic labeling periods of 2, 4, or 7 days revealed up to a doubling of the measured synthesis rate in the shorter labeling period compared with the longer period of labeling. From our model, we conclude that a 4-wk period of labeling is ideal for considering all proteins in a mixed-tissue fraction, while minimizing the slowing effect of fully turned-over proteins. In addition, we advocate that careful consideration must be paid to the period of isotopic labeling when comparing mixed protein synthetic rates between studies.

APA, Harvard, Vancouver, ISO, and other styles

3

Dudley, M. A., F. Jahoor, D. G. Burrin, and P. J. Reeds. "Brush-border disaccharidase synthesis in infant pigs measured in vivo with [2H3]leucine." American Journal of Physiology-Gastrointestinal and Liver Physiology 267, no. 6 (December 1, 1994): G1128—G1134. http://dx.doi.org/10.1152/ajpgi.1994.267.6.g1128.

Full text

Abstract:

Conscious unrestrained piglets were fasted overnight and infused intravenously with [2H3]leucine for 6 h. Sucrase isomaltase and lactase phlorizin hydrolase were immunoprecipitated from jejunal mucosal membranes, and the immunoprecipitates were electrophoresed on polyacrylamide gels. Bands corresponding to the pro and mature isoforms of both enzymes were acid hydrolyzed. [2H3]leucine isotopic enrichment was measured by gas chromatography-mass spectrometry using negative chemical ionization. Plasma leucine reached isotopic steady state within 90 min. The isotopic enrichment of mucosal leucine was 73% of that of plasma leucine. The high mannose and complex glycosylated forms of prolactase were in isotopic equilibrium, and their isotopic enrichment was 94% of mucosal leucine. The fractional synthesis rates of total and membrane protein were 0.45 and 0.65 days-1, whereas the processing rates of mature lactase, sucrase, and isomaltase were 0.90, 0.23, and 0.21 days-1, respectively. Approximately 65% of the label in the sucrase isomaltase immunoprecipitate was in the complex glycosylated precursor, whereas 73% of the label in lactase phlorizin hydrolase was in the mature (160 kDa) form. We conclude that the low rate of brush-border sucrase synthesis reflects a slow rate at which the complex glycosylated precursor is processed to the brush-border form.

APA, Harvard, Vancouver, ISO, and other styles

4

Eglinton, T. I., M. A. Goñi, J. J. Boon, E. R. E. van der Hage, N. Terashima, and Y. Xie. "Incorporation of 13C-Labeled Coniferyl Alcohol into Developing Ginkgo biloba L. Lignin Revealed by Analytical Pyrolysis and CuO Oxidation in Combination with Isotope Ratio Monitoring-Gas Chromatography-Mass Spectrometry." Holzforschung 54, no. 1 (January 28, 2000): 39–54. http://dx.doi.org/10.1515/hf.2000.007.

Full text

Abstract:

Summary A suite of four samples of xylem tissue from Ginkgo (Ginkgo biloba L.) shoots grown in a medium containing coniferin 13C-labeled at differing side-chain carbon atoms were studied using thermal and chemical degradation methods in combination with molecular-level isotopic analyses. The aims of the study were threefold: (1) to verify conclusions drawn from Nuclear Magnetic Resonance experiments previously performed on the same tissue samples, (2) to investigate degradation mechanisms and (3) to quantify the proportion of labeled material in each sample. Isotopic analysis of specific degradation products revealed the presence of the label exclusively within lignin-derived (phenolic) products and that the label is retained in its original position on the side-chain. These two results clearly indicate that there is no “scrambling” of carbon atoms as a result of thermal or chemical degradation, and thus lend strong support to analytical pyrolysis and chemolysis as viable approaches for structural investigations of the lignin macromolecule. Indeed, the isotopic enrichment of specific degradation products provides new evidence for certain types of linkages within the lignin polymer. The distribution and isotopic composition of the degradation products also strongly suggest an origin from newly-formed lignin as opposed to DHP-type products or unreacted substrate. As such, the data provides added confidence in the selective labeling approach for elucidation of the structure and biosynthesis of lignin. Isotopic mass balance calculations reveal that certain pyrolysis and CuO oxidation products show enhanced labeling which may be indicative of preferential incorporation of their specific precursors into the growing lignin macromolecule or heterogeneous lignin deposition.

APA, Harvard, Vancouver, ISO, and other styles

5

Studer, M. S., R. T. W. Siegwolf, M. Leuenberger, and S. Abiven. "Multi-isotope labelling (13C, 18O, 2H) of fresh assimilates to trace organic matter dynamics in the plant-soil system." Biogeosciences Discussions 11, no. 11 (November 18, 2014): 15911–43. http://dx.doi.org/10.5194/bgd-11-15911-2014.

Full text

Abstract:

Abstract. Isotope labelling is a powerful tool to study elemental cycling within terrestrial ecosystems. Here we describe a new multi-isotope technique to label organic matter (OM). We exposed poplars (Populus deltoides x nigra) for 14 days to an atmosphere enriched in 13CO2 and depleted in 2H218O. After one week, the water-soluble leaf OM (δ13C = 1346 ± 162‰) and the leaf water were strongly labelled (δ18O = −63± 8‰, δ2H = −156 ± 15‰). The leaf water isotopic composition was between the atmospheric and stem water, indicating a considerable diffusion of vapour into the leaves (58–69%). The atomic ratios of the labels recovered (18O/13C, 2H/13C) were 2–4 times higher in leaves than in the stems and roots. This either indicates the synthesis of more condensed compounds (lignin vs. cellulose) in roots and stems, or be the result of O and H exchange and fractionation processes during transport and biosynthesis. We demonstrate that the three major OM elements (C, O, H) can be labelled and traced simultaneously within the plant. This approach could be of interdisciplinary interest for the fields of plant physiology, paleoclimatic reconstruction or soil science.

APA, Harvard, Vancouver, ISO, and other styles

6

Romsdahl, Trevor B., Shrikaar Kambhampati, Somnath Koley, Umesh P. Yadav, Ana Paula Alonso, Doug K. Allen, and Kent D. Chapman. "Analyzing Mass Spectrometry Imaging Data of 13C-Labeled Phospholipids in Camelina sativa and Thlaspi arvense (Pennycress) Embryos." Metabolites 11, no. 3 (March 4, 2021): 148. http://dx.doi.org/10.3390/metabo11030148.

Full text

Abstract:

The combination of 13C-isotopic labeling and mass spectrometry imaging (MSI) offers an approach to analyze metabolic flux in situ. However, combining isotopic labeling and MSI presents technical challenges ranging from sample preparation, label incorporation, data collection, and analysis. Isotopic labeling and MSI individually create large, complex data sets, and this is compounded when both methods are combined. Therefore, analyzing isotopically labeled MSI data requires streamlined procedures to support biologically meaningful interpretations. Using currently available software and techniques, here we describe a workflow to analyze 13C-labeled isotopologues of the membrane lipid and storage oil lipid intermediate―phosphatidylcholine (PC). Our results with embryos of the oilseed crops, Camelina sativa and Thlaspi arvense (pennycress), demonstrated greater 13C-isotopic labeling in the cotyledons of developing embryos compared with the embryonic axis. Greater isotopic enrichment in PC molecular species with more saturated and longer chain fatty acids suggest different flux patterns related to fatty acid desaturation and elongation pathways. The ability to evaluate MSI data of isotopically labeled plant embryos will facilitate the potential to investigate spatial aspects of metabolic flux in situ.

APA, Harvard, Vancouver, ISO, and other styles

7

BLUCK, Leslie J. C., Allan T. CLAPPERTON, Cheryl V. KIDNEY, and W. Andy COWARD. "Glycogenesis and glucose oxidation during an intravenous glucose tolerance test in man." Clinical Science 106, no. 6 (June 1, 2004): 645–52. http://dx.doi.org/10.1042/cs20030353.

Full text

Abstract:

The quantity of deuterated glucose customarily given in labelled IVGTTs (intravenous glucose tolerance tests) changes the isotopic composition of the subject's body water enough to be detected by mass spectrometric techniques. Glucose undergoing direct glycogenesis does not contribute label to the body water pool, and isotope incorporated into it must have come from glucose that has either been oxidized or undergone indirect glycogenesis. By subtracting the amount of label found in body water from the total amount of glucose utilized, as calculated from the minimal model of glucose disappearance, it should be possible to study the partitioning of the dose given between direct glycogenesis in skeletal muscle and other metabolic pathways. To establish these principles, we used isotope ratio MS to determine body water composition in groups of healthy (n=7; mean weight, 76 kg; fasting plasma glucose and insulin, 5.1 mmol and 40 pmol respectively) and Type II diabetic (n=5; mean weight, 84 kg; fasting plasma glucose and insulin, 6.2 mmol and 75 pmol respectively) subjects undergoing IVGTTs. It was found that, for healthy subjects, 31% of the dose given was utilized in direct glycogenesis and this was decreased to 15% in diabetes. Defects in muscle glycogen synthesis in diabetes of the same order are well known from magnetic resonance studies. We conclude that measurement of label incorporation into body water is potentially useful for investigation of the metabolism of a glucose load in vivo during an IVGTT.

APA, Harvard, Vancouver, ISO, and other styles

8

Studer, M. S., R. T. W. Siegwolf, M. Leuenberger, and S. Abiven. "Multi-isotope labelling of organic matter by diffusion of 2H/18O-H2O vapour and 13C-CO2 into the leaves and its distribution within the plant." Biogeosciences 12, no. 6 (March 20, 2015): 1865–79. http://dx.doi.org/10.5194/bg-12-1865-2015.

Full text

Abstract:

Abstract. Isotope labelling is a powerful tool to study elemental cycling within terrestrial ecosystems. Here we describe a new multi-isotope technique to label organic matter (OM). We exposed poplars (Populus deltoides × nigra) for 14 days to an atmosphere enriched in 13CO2 and depleted in 2H218O. After 1 week, the water-soluble leaf OM (δ13C = 1346 ± 162‰) and the leaf water were strongly labelled (δ18O = −63 ± 8, δ2H = −156 ± 15‰). The leaf water isotopic composition was between the atmospheric and stem water, indicating a considerable back-diffusion of vapour into the leaves (58–69%) in the opposite direction to the net transpiration flow. The atomic ratios of the labels recovered (18O/13C, 2H/13C) were 2–4 times higher in leaves than in the stems and roots. This could be an indication of the synthesis of more condensed compounds in roots and stems (e.g. lignin vs. cellulose) or might be the result of O and H exchange and fractionation processes during phloem transport and biosynthesis. We demonstrate that the three major OM elements (C, O, H) can be labelled and traced simultaneously within the plant. This approach could be of interdisciplinary interest in the fields of plant physiology, palaeoclimatic reconstruction or soil science.

APA, Harvard, Vancouver, ISO, and other styles

9

Dimitrova, Tsvetelina, Frank Repmann, and Dirk Freese. "Preparation of 15N-labeled Potassium Ferrocyanide for Tracer Studies." Environment and Pollution 6, no. 2 (September 29, 2017): 41. http://dx.doi.org/10.5539/ep.v6n2p41.

Full text

Abstract:

Isotopic labels are widely used to trace the fate and cycling of common environmental contaminants. Many of the labeled materials are not available commercially and, depending on the complexity of the substance, the label and the enrichment level, custom syntheses are costly. A simple, straightforward, and cost effective method for the preparation of a highly enriched, 15N-labeled potassium ferrocyanide (K4[Fe(C15N)6]*3H2O) has been developed to meet the requirements of related tracer experiments and minimize their costs. In this case, the 15N label was used to quantify iron cyanide detoxification (biodegradation and/or transformation) within soil-plant-systems. 15N-labeled potassium cyanide (KC15N) and a ferrous iron salt have been used for the synthesis. Extensive qualitative and quantitative analyses showed a product, entirely identical in its functional and elemental components to commercial non-labeled K4[Fe(CN)6]*3H2O and in its 15N enrichment to the KC15N used for its synthesis. To investigate their behavior and fate in various environmental compartments, other labeled iron or metal cyanide complexes might be synthesized in analogous manner.

APA, Harvard, Vancouver, ISO, and other styles

10

Sheveleva, Nadezhda N., Denis A. Markelov, Mikhail A. Vovk, Irina I. Tarasenko, Mariya E. Mikhailova, Maxim Yu Ilyash, Igor M. Neelov, and Erkki Lahderanta. "Stable Deuterium Labeling of Histidine-Rich Lysine-Based Dendrimers." Molecules 24, no. 13 (July 6, 2019): 2481. http://dx.doi.org/10.3390/molecules24132481.

Full text

Abstract:

Peptide dendrimers, due to their biocompatibility and low toxicity, are highly promising candidates as nanocarriers for drugs and genes. The development of this kind of delivery system requires reliable monitoring of their metabolic and biological pathways. In this respect, hydrogen isotope labeling has tremendous importance, being a safe tool for detection of the labeled nanocarriers. In this work, we have synthesized new histidine-rich lysine-based dendrimers (Lys-2His dendrimer) with two linear histidine (His) residues in every inner segment. The presence of His residues has enabled us to perform controlled deuteration of Lys-2His dendrimers. The high deuteration degree (around 70%) does not practically change after redissolving the samples in H2O and heating them at 40 °C, which indicates the isotopic label stability.

APA, Harvard, Vancouver, ISO, and other styles

11

Varma, V. A., C. M. Cerjan, K. L. Abbott, and S. B. Hunter. "Non-isotopic in situ hybridization method for mitochondria in oncocytes." Journal of Histochemistry & Cytochemistry 42, no. 2 (February 1994): 273–76. http://dx.doi.org/10.1177/42.2.8288868.

Full text

Abstract:

We used in situ hybridization to specifically identify mitochondria in a series of formalin-fixed, paraffin-embedded oncocytic lesions. Digoxigenin-labeled DNA probes were generated by the polymerase chain reaction (PCR), with primers designed to amplify a mitochondrion-specific 154 BP sequence within the ND4 coding region. Probes were hybridized with mitochondrial DNA under stringent conditions. Oncocytes were strongly and consistently stained, reflecting the high copy number of mitochondrial DNA within these cells. Because of the presence of endogenous biotin within mitochondria, digoxigenin is preferable to biotin as a label for detection of mitochondria.

APA, Harvard, Vancouver, ISO, and other styles

12

Thies, R. S., and L. J. Mandel. "Role of glucose in corneal metabolism." American Journal of Physiology-Cell Physiology 249, no. 5 (November 1, 1985): C409—C416. http://dx.doi.org/10.1152/ajpcell.1985.249.5.c409.

Full text

Abstract:

Glucose catabolism by glycolysis and the Krebs cycle was examined in the isolated rabbit cornea incubated with [6-14C]glucose. The production of [14C]lactate and 14CO2 from this substrate provided minimal values for the fluxes through these pathways since the tissue was in metabolic steady state but not isotopic steady state during the 40-min incubation. The specific activity of lactate under these conditions was one-third of that for [6-14C]glucose, and label dilution by exchange with unlabeled alanine was minimal, suggesting that glycogen degradation was primarily responsible for this dilution of label in the Embden-Meyerhof pathway. In addition, considerable label accumulation was found in glutamate and aspartate. Calculations revealed that these endogenous amino acid pools were not isotopically equilibrated after the incubation period, suggesting that they were responsible for the isotopic nonsteady state by exchange dilution through transaminase reactions with labeled intermediates. An estimate of glucose oxidation by the Krebs cycle, which was corrected for label dilution by exchange, indicated that glucose could account for most of the measured corneal oxygen consumption that was coupled to oxidative phosphorylation. A minor component of this respiration could not be accounted for by glucose or glycogen oxidation. Additional experiments suggested that endogenous fatty acid oxidation was probably also active under these conditions. Finally, reciprocal changes in plasma membrane Na+-K+-ATPase activity induced by ouabain and nystatin were found to concomitantly alter oxygen consumption rates and [14C]lactate production from [6-14C]glucose. These results demonstrated the capacity for regulating glycolysis and the Krebs cycle in response to changing energy demands in the cornea.

APA, Harvard, Vancouver, ISO, and other styles

13

Parshina, N. I., Sh K. Kasymov, O. N. Veshkurova, A. A. Takanaev, and Sh I. Salikhov. "Use of various modifying agents for introduction of an isotopic label into cellulose." Chemistry of Natural Compounds 25, no. 6 (November 1989): 731–32. http://dx.doi.org/10.1007/bf00598287.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Harvey, Linda J., Gosia Majsak-Newman, Jack R. Dainty, D. John Lewis, Nicola J. Langford, Helen M. Crews, and Susan J. Fairweather-Tait. "Adaptive responses in men fed low- and high-copper diets." British Journal of Nutrition 90, no. 1 (July 2003): 161–68. http://dx.doi.org/10.1079/bjn2003887.

Full text

Abstract:

The study of Cu metabolism is hampered by a lack of sensitive and specific biomarkers of status and suitable isotopic labels, but limited information suggests that Cu homeostasis is maintained through changes in absorption and endogenous loss. The aim of the present study was to employ stable-isotope techniques to measure Cu absorption and endogenous losses in adult men adapted to low, moderate and high Cu-supplemented diets. Twelve healthy men, aged 20–59 years, were given diets containing 0·7, 1·6 and 6·0 mg Cu/d for 8 weeks, with at least 4 weeks intervening washout periods. After 6 weeks adaptation, apparent and true absorption of Cu were determined by measuring luminal loss and endogenous excretion of Cu following oral administration of 3 mg highly enriched65Cu stable-isotope label. Apparent and true absorption (41 and 48% respectively) on the low-Cu diet were not significantly different from the high-Cu diet (45 and 48% respectively). Endogenous losses were significantly reduced on the low- (0·45mg/d;P<0·001) and medium- (0·81 mg/d;P=0·001) compared with the high-Cu diet (2·46mg/d). No biochemical changes resulting from the dietary intervention were observed. Cu homeostasis was maintained over a wide range of intake and more rapidly at the lower intake, mainly through changes in endogenous excretion.

APA, Harvard, Vancouver, ISO, and other styles

15

Pang, Xibin, Chuncheng Chen, Hongwei Ji, Yanke Che, Wanhong Ma, and Jincai Zhao. "Unraveling the Photocatalytic Mechanisms on TiO2 Surfaces Using the Oxygen-18 Isotopic Label Technique." Molecules 19, no. 10 (October 10, 2014): 16291–311. http://dx.doi.org/10.3390/molecules191016291.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

de Graaf, Robin A., Monique A. Thomas, Kevin L. Behar, and Henk M. De Feyter. "Characterization of Kinetic Isotope Effects and Label Loss in Deuterium-Based Isotopic Labeling Studies." ACS Chemical Neuroscience 12, no. 1 (December 15, 2020): 234–43. http://dx.doi.org/10.1021/acschemneuro.0c00711.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Gopius, E. D., M. L. Karpyuk, T. A. Smolina, and O. A. Reutov. "Study of the mechanism of isomerization of 2-bromopropyl benzoate using an18O isotopic label." Bulletin of the Academy of Sciences of the USSR Division of Chemical Science 37, no. 9 (September 1988): 1925–26. http://dx.doi.org/10.1007/bf00962515.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Halpern, Howard J., Miroslav Peril, Thanh-D. Nguyen, David P. Spencer, Beverly A. Teicher, Yawares J. Lin, and Michael K. Bowman. "Selective isotopic labeling of a nitroxide spin label to enhance sensitivity for T2 oxymetry." Journal of Magnetic Resonance (1969) 90, no. 1 (October 1990): 40–51. http://dx.doi.org/10.1016/0022-2364(90)90364-f.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Sidossis, L. S., A. R. Coggan, A. Gastaldelli, and R. R. Wolfe. "A new correction factor for use in tracer estimations of plasma fatty acid oxidation." American Journal of Physiology-Endocrinology and Metabolism 269, no. 4 (October 1, 1995): E649—E656. http://dx.doi.org/10.1152/ajpendo.1995.269.4.e649.

Full text

Abstract:

The purpose of this study was to acquire a new correction factor for use in tracer estimations of plasma fatty acid oxidation that would fully account for label fixation during the infusion of fatty acid tracers. Thus volunteers were infused with 13C-labeled fatty acids and [1-14C]acetate in the basal state, during hyperinsulinemia-hyperglycemia (clamp), and during 1 h of cycling exercise. The fractional recovery of acetate label (i.e., the acetate correction factor) was 0.56 +/- 0.02, 0.50 +/- 0.03, and 0.80 +/- 0.03 in the basal state and during the clamp and exercise, respectively. Isotopically determined plasma fatty acid oxidation rates (mumol.kg-1.min-1) were 1.7 +/- 0.2, 0.8 +/- 0.2, and 6.4 +/- 0.5 (no correction); 2.1 +/- 0.2, 1.0 +/- 0.2, and 6.7 +/- 0.5 (bicarbonate correction); and 3.1 +/- 0.2, 1.5 +/- 0.2, and 8.2 +/- 0.4 (acetate correction). We conclude that use of the acetate correction factor in place of the bicarbonate correction factor should improve the accuracy of isotopic measurements of plasma fatty acid oxidation, because it accounts for label fixation that might occur at any step between the entrance of labeled acetyl-CoA into the tricarboxylic acid cycle until the recovery of label in breath CO2.

APA, Harvard, Vancouver, ISO, and other styles

20

Stabler, T. V., and A. L. Siegel. "Chemiluminescence immunoassay of aldosterone in serum." Clinical Chemistry 37, no. 11 (November 1, 1991): 1987–89. http://dx.doi.org/10.1093/clinchem/37.11.1987.

Full text

Abstract:

Abstract A chemiluminescence immunoassay (CLI) for the direct measurement of aldosterone in serum was developed with aminobutylethyl isoluminol (ABEI) as the label. In this competitive assay the samples are incubated with sample, antibody, aldosterone-carboxymethyl oxime-ABEI, and paramagnetic particles coated with second antibody. After magnetic separation and washing, the samples are incubated with 200 microL of NaOH (2 mol/L) at 60 degrees C for 30 min. In the luminometer the chemiluminescence is produced by the serial injection of 150 microL each of microperoxidase and H2O2 solutions. Comparison of results with an RIA method showed excellent agreement: CLI = 1.001 RIA + 0.020 (r = 0.99, n = 93). The method is simple and avoids the hazards and costs associated with isotopic waste. The label has a shelf life of at least two years.

APA, Harvard, Vancouver, ISO, and other styles

21

Říčný, Jan, Libuše Šimková, and Angela Vincent. "Determination of Anti-Acetylcholine Receptor Antibodies in Myasthenic Patients by Use of Time-resolved Fluorescence." Clinical Chemistry 48, no. 3 (March 1, 2002): 549–54. http://dx.doi.org/10.1093/clinchem/48.3.549.

Full text

Abstract:

Abstract Background: Autoantibodies against nicotinic acetylcholine receptor (nAChR) in myasthenia gravis (MG) patients are usually detected by radioimmunoprecipitation assays using extracted acetylcholine receptors labeled irreversibly with 125I-α-bungarotoxin (α-BuTx). To provide a nonradioactive immunoassay, we established an assay using nAChRs labeled with Eu3+-α-cobratoxin (α-CTx). Methods: We derivatized α-CTx with a diethylenetriaminepentaacetate moiety and formed a complex with Eu3+. The complex was purified by HPLC, and the fractions were tested for binding to Torpedo and human nAChRs. The most active fractions were used to label nAChRs for the immunoprecipitation assay, and the bound Eu3+ was quantified by time-resolved fluorescence. Results: Eu3+-labeled α-CTx competed with 125I-α-BuTx for binding to Torpedo nAChRs and saturated the binding sites of human nAChRs, with a Kd of 7.2 × 10−9 mol/L. Results of the immunoassay performed with Eu3+-labeled α-CTx were similar to those obtained with 125I-α-BuTx, with a slightly higher limit of detection [0.3 nmol/L (n = 6) vs ∼0.1 nmol/L for isotopic assay]. None of 34 negative sera tested (16 healthy controls, 10 patients with nonmyasthenia-related disease, 8 patients seronegative for MG) gave a value >0.3 nmol/L. Of the 35 positive myasthenic sera (with antibody values, previously determined by isotopic assay, of 0.4–1290 nmol/L) compared in the two assays, 32 tested positive with the Eu3+ assay. Linear regression analysis yielded the equation: y = 1.035x − 0.013 nmol/L; Sy|x = 0.172 nmol/L; r2 = 0.977. Conclusions: The new time-resolved fluorescence method for quantification of antibodies to nAChRs in MG patients provides a performance similar to that of the widely used isotopic assay and could be used in laboratories with restricted use of isotopes.

APA, Harvard, Vancouver, ISO, and other styles

22

Griffey, R. H., M. A. Jarema, S. Kunz, P. R. Rosevear, and A. G. Redfield. "Isotopic-label-directed observation of the nuclear Overhauser effect in poorly resolved proton NMR spectra." Journal of the American Chemical Society 107, no. 3 (February 1985): 711–12. http://dx.doi.org/10.1021/ja00289a037.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Johnson, A. W., J. M. Berrington, I. Walker, A. Manning, and M. S. Losowsky. "Measurement of the transfer of the nitrogen moiety of intestinal lumen glutamic acid in man after oral ingestion of l-[15N]glutamic acid." Clinical Science 75, no. 5 (November 1, 1988): 499–502. http://dx.doi.org/10.1042/cs0750499.

Full text

Abstract:

1. The measurement of the intestinal metabolism of the nitrogen moiety of glutamic acid has been investigated by oral ingestion of l-[15N]glutamic acid and sampling of arterialized blood. 2. Measurements have been made in six normal adults weighing an average of 72.8 kg ingesting 100 mg of l-[15N]glutamic acid after an overnight fast. 3. Measurement of the enrichment of arterial glutamic acid, glutamine and alanine was by gas chromatography–mass spectrometry. Isotopic enrichment of the amino acids was followed for 150 min after the ingestion of the amino acid. 4. Arterialized venous blood amino acid concentrations, measured by h.p.l.c., demonstrated no significant changes during the course of the experiment. 5. From the observed appearance of label in arterialized glutamic acid, alanine and glutamine, little luminal glutamic acid reaches the extracellular pool. The majority of the administered nitrogen label appears in the arterial alanine and glutamine components.

APA, Harvard, Vancouver, ISO, and other styles

24

Hunter, W. R., A. Jamieson, V. A. I. Huvenne, and U. Witte. "Food quality determines sediment community responses to marine vs. terrigenous organic matter in a submarine canyon." Biogeosciences Discussions 9, no. 8 (August 22, 2012): 11331–74. http://dx.doi.org/10.5194/bgd-9-11331-2012.

Full text

Abstract:

Abstract. The Whittard canyon is a branching submarine canyon on the Celtic continental margin, which may act as a conduit for sediment and organic matter (OM) transport from the European continental slope to the abyssal sea floor. In situ stable-isotope labelling experiments were conducted in the eastern and western branches of the Whittard canyon testing short term (3–7 day) responses of sediment communities to deposition of nitrogen-rich marine (Thallassiosira weissflogii) and nitrogen-poor terrigenous (Triticum aestivum) phytodetritus. 13C and 15N labels were traced into faunal biomass and bulk sediments, and the 13C label traced into bacterial polar lipid fatty acids (PLFAs). Isotopic labels penetrated to 5 cm sediment depth, with no differences between stations or experimental treatments (substrate or time). Macrofaunal assemblage structure differed between the eastern and western canyon branches. Following deposition of marine phytodetritus, no changes in macrofaunal feeding activity were observed between the eastern and western branches, with little change between 3 and 7 days. Macrofaunal C and N uptake was substantially lower following deposition of terrigenous phytodetritus with feeding activity governed by a strong N demand. Bacterial C uptake was greatest, in the western branch of the Whittard canyon, but feeding activity decreased between 3 and 7 days. Bacterial processing of marine and terrigenous OM were similar to the macrofauna in surficial (0–1 cm) sediments. However, in deeper sediments bacteria utilised greater proportions of terrigenous OM. Bacterial biomass decreased following phytodetritus deposition and was negatively correlated to macrofaunal feeding activity. Consequently, this study suggests that macrofaunal-bacterial interactions influence benthic C cycling in the Whittard canyon, resulting in differential fates for marine and terrigenous OM.

APA, Harvard, Vancouver, ISO, and other styles

25

Hunter, W. R., A. Jamieson, V. A. I. Huvenne, and U. Witte. "Sediment community responses to marine vs. terrigenous organic matter in a submarine canyon." Biogeosciences 10, no. 1 (January 8, 2013): 67–80. http://dx.doi.org/10.5194/bg-10-67-2013.

Full text

Abstract:

Abstract. The Whittard Canyon is a branching submarine canyon on the Celtic continental margin, which may act as a conduit for sediment and organic matter (OM) transport from the European continental slope to the abyssal sea floor. In situ stable-isotope labelling experiments were conducted in the eastern and western branches of the Whittard Canyon, testing short-term (3–7 days) responses of sediment communities to deposition of nitrogen-rich marine (Thalassiosira weissflogii) and nitrogen-poor terrigenous (Triticum aestivum) phytodetritus. 13C and 15N labels were traced into faunal biomass and bulk sediments, and the 13C label traced into bacterial polar lipid fatty acids (PLFAs). Isotopic labels penetrated to 5 cm sediment depth, with no differences between stations or experimental treatments (substrate or time). Macrofaunal assemblage structure differed between the eastern and western canyon branches. Following deposition of marine phytodetritus, no changes in macrofaunal feeding activity were observed between the eastern and western branches, with little change between 3 and 7 days. Macrofaunal C and N uptake was substantially lower following deposition of terrigenous phytodetritus with feeding activity governed by a strong N demand. Bacterial C uptake was greatest in the western branch of the Whittard Canyon, but feeding activity decreased between 3 and 7 days. Bacterial processing of marine and terrigenous OM were similar to the macrofauna in surficial (0–1 cm) sediments. However, in deeper sediments bacteria utilised greater proportions of terrigenous OM. Bacterial biomass decreased following phytodetritus deposition and was negatively correlated to macrofaunal feeding activity. Consequently, this study suggests that macrofaunal–bacterial interactions influence benthic C cycling in the Whittard Canyon, resulting in differential fates for marine and terrigenous OM.

APA, Harvard, Vancouver, ISO, and other styles

26

O'Keefe, IH, LF Sharry, and BA Panaretto. "The Fate of Tritiated rm-Epidermal Growth Factor in the Sheep: Validation of the Labelling Procedure and Rate of Tissue Clearance." Australian Journal of Biological Sciences 41, no. 4 (1988): 539. http://dx.doi.org/10.1071/bi9880539.

Full text

Abstract:

Plasmid-derived recombinant mouse epidermal growth factor, rm-EGF, was purified by ion pair reversed phase high performance liquid chromatography. The product peak (termed rm-a-EGF) was characterized by physicochemical techniques including fast atom bombardment mass spectrometry, high field proton magnetic resonance and amino acid sequencing (amino acid arrangement and composition). The rm-a-EGF was tritiated, labile tritium removed by lyophilization: and the product purified and characterized as for the parent compound to yield a compound identical to rm-a-EGF except for the isotopic hydrogen substitution. Label stability was validated by lyophilization of samples, especially urine.

APA, Harvard, Vancouver, ISO, and other styles

27

Kien, C. L., K. Ault, and R. E. McClead. "In vivo estimation of lactose hydrolysis in premature infants using a dual stable tracer technique." American Journal of Physiology-Endocrinology and Metabolism 263, no. 5 (November 1, 1992): E1002—E1009. http://dx.doi.org/10.1152/ajpendo.1992.263.5.e1002.

Full text

Abstract:

To investigate their putative capacity for lactose digestion, primed continuous orogastric infusions of [1-13C]glucose and D-[1-13C]lactose were administered on consecutive days to five premature infants (30–31 wk gestation, 15–32 days of age), who were fed by orogastric infusions of human milk or formula. By monitoring the plateau isotopic enrichment of plasma glucose using isotopomers containing the entire derivatized glucose molecule or C-2 through C-6, we were able to distinguish label appearing in the peripheral circulation deriving from unmetabolized glucose from that arising from recycled or fermented glucose (or lactose). Isotopic enrichment of the C-1 of glucose, corrected for recycling, was then calculated during each tracer infusion, and the fraction of dietary lactose subjected to in vivo hydrolysis was estimated from these values and the respective tracer infusion rates, assuming similar absorptive and metabolic fates of labeled glucose arising from either tracer. This fraction averaged 1.02 +/- 0.16 (SD), suggesting that lactose digestion is efficient by 34-wk postconceptional age.

APA, Harvard, Vancouver, ISO, and other styles

28

Finglas, Paul Michael, David Hart, Caroline Wolfe, Anthony John Aaron Wright, Sue Southon, Fred Mellon, Hanneke van den Akker, and Kees de Meer. "Validity of Dual-Label Stable Isotopic Protocols and Urinary Excretion Ratios to Determine Folate Bioavailability from Food." Food and Nutrition Bulletin 23, no. 3_suppl1 (January 2002): 107–12. http://dx.doi.org/10.1177/15648265020233s121.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Angel, Peggi M., and Ron Orlando. "Trypsin is the primary mechanism by which the 18O isotopic label is lost in quantitative proteomic studies." Analytical Biochemistry 359, no. 1 (December 2006): 26–34. http://dx.doi.org/10.1016/j.ab.2006.08.036.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Miller, P. E., and J. W. Adelson. "Proteins are secreted from heterogeneous prestored sources in the exocrine pancreas." American Journal of Physiology-Gastrointestinal and Liver Physiology 252, no. 6 (June 1, 1987): G768—G775. http://dx.doi.org/10.1152/ajpgi.1987.252.6.g768.

Full text

Abstract:

Recent studies demonstrating nonparallel regulated secretion of prestored digestive enzymes in tightly linked groups consistent with the exocytosis mechanism led us to predict that digestive enzymes would be found to be secreted from heterogeneous sources within the exocrine pancreas (J. W. Adelson, and P.E. Miller, Science Wash. DC 228: 993-996, 1985). We explored whether the gland was heterogeneous with respect to its sources of prestored secretory proteins with a double isotopic label method not dependent on activity of secreted digestive enzymes. Rabbit pancreatic proteins were double labeled in vivo by injection of each animal with chemically identical but isotopically distinct mixtures of 3H- and 14C-labeled amino acids, which were administered separately or together on consecutive days after partial depletion of prestored proteins by administration of cholecystokinin (CCK), methacholine chloride, or saline in a protocol in which order of both isotope and secretagogue administration was varied. Three days after labeling, proteins were recovered by collection from cannulated pancreatic ducts of anesthetized animals after stimulation with alternating increasing doses of CCK and methacholine chloride. Pooled secretory data were analyzed to determine whether secretagogue pretreatment resulted in specific and heterogeneous sequestration of proteins after synthesis; data after final secretory stimulation with methacholine chloride and CCK were individually analyzed to determine whether presequestered proteins were mobilized from heterogeneous compartments during secretion. Correlation and regression analysis of isotopic outputs and variance analysis of specific radioactivities of secreted proteins showed sequestration into and secretion from heterogeneous pools of secretory proteins, directly confirming out hypothesis. These results provide a cell biological mechanism explaining regulated nonparallel secretion of digestive enzymes.

APA, Harvard, Vancouver, ISO, and other styles

31

Yacob, Sara, Michael J. Caulfield, and Timothy A. Barckholtz. "Partial oxidation of alkanes by dioxiranes formed in situ at low temperature." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, no. 2110 (November 27, 2017): 20170055. http://dx.doi.org/10.1098/rsta.2017.0055.

Full text

Abstract:

Partial oxidation catalysts capable of efficiently operating at low temperatures may limit the over-oxidation of alkane substrates and thereby improve selectivity. This work focuses on examining alkane oxidation using completely metal-free organocatalysts, dioxiranes. The dioxiranes employed here are synthesized by oxidation of a ketone using a terminal oxidant, such as hydrogen peroxide. Our work generates the dioxirane in situ , so that the process can be catalytic with respect to the ketone. To date, we have demonstrated selective partial oxidation of adamantane using ketone catalysts resulting in yields upwards of 60% towards 1-adamantanol with greater than 99% selectivity. Furthermore, we have demonstrated that changing the electrophilic character of the ketone R groups to contain more electron-donating ligands facilitates the dioxirane ring formation and improves overall oxidation yields. Isotopic labelling studies using H 2 18 O 2 show the preferential incorporation of an 18 O label into the parent ketone, providing evidence for a dioxirane intermediate formed in situ . The isotopic labelling studies, along with solvent effect studies, suggest the formation of peracetic acid as a reactive intermediate. This article is part of a discussion meeting issue ‘Providing sustainable catalytic solutions for a rapidly changing world’.

APA, Harvard, Vancouver, ISO, and other styles

32

Bäurle, Wolfgang, Herbert Brösicke, Dwight E. Matthews, Karin Pogan, and Peter Fürst. "Metabolism of parenterally administered fat emulsions in the rat: studies of fatty acid oxidation with 1-13C- and 8-13C-labelled triolein." British Journal of Nutrition 79, no. 4 (April 1998): 381–87. http://dx.doi.org/10.1079/bjn19980063.

Full text

Abstract:

To reassess the hypothesis that fatty acid catabolism occurs to completion via β-oxidation, male Sprague–Dawley rats receiving continuous total parenteral nutrition (TPN) including 43% energy as fat were infused with [1-13C]- or [8-13C]triolein. Expired CO2 was collected continuously for 4 h and its 13C: 12C ratio determined by isotope–ratio mass spectrometry. Bicarbonate retention was also assessed over 4 h by infusion of NaH14CO3 and measurement of the expired 14CO2. A possible loss of label from [8-13C]oleic acid from the citric acid cycle via labelled acetyl-CoA without oxidation to CO2 was assessed by infusing further animals with acetate labelled with 14C either at C atoms 1 or 2 and determination of its conversion to expired 14CO2. At isotopic steady state, 63.2 (SE 1.6)% (n 8) of the infused [1-14C]acetate and 46.0 (SE 1.2)% (n 8) of [2-14C]acetate was recovered as expired 14CO2. After correction for bicarbonate retention and non-oxidative isotope loss, 37.3 (SE 1.2)% (n 20) of the [1-13C]triolein was found to have been oxidized, whereas 32.6 (SE 1.0)% (n 20) of the [8-13C]triolein was oxidized (P ≤ 0.01). The lower oxidation of the C atom at position 8 of oleic acid than that at position 1 indicates incomplete oxidative breakdown of the fatty acid after entering β-oxidation.

APA, Harvard, Vancouver, ISO, and other styles

33

Newell, Evan, Natalia Sigal, Sean Bendall, Garry Nolan, and Mark Davis. "Profiling antigen-specific T cell phenotypes with heavy metal labeled peptide-Major Histocompatibility Complex tetramers and single cell mass-spectroscopy (CyTOF) (65.40)." Journal of Immunology 186, no. 1_Supplement (April 1, 2011): 65.40. http://dx.doi.org/10.4049/jimmunol.186.supp.65.40.

Full text

Abstract:

Abstract The direct detection of antigen-specific T cells using fluorescently tagged pMHC-tetramers is widely used in basic and clinical immunology, allowing the unperturbed assessment of T cell phenotypes by concurrent staining with surface and/or intracellular markers. However, the number of T cell specificities and phenotypic markers that can be assessed in a single sample is limited by fluorescence spectral overlap. We recently devised a way to label pMHC tetramers with heavy metals that allows for detection using single-cell mass spectroscopy (Cytometry via Time of Flight - CyTOF). The ability to use 30+ different isotopic labels in this system greatly extends the number of T cell specificities, phenotypic markers and intracellular cytokines that can be simultaneously evaluated. Using this approach, we find that CD8+ T cells from human blood display a much broader diversity of phenotypes and cytokine production capabilities than previously appreciated. Although the phenotypes for different pathogen specific T cells are diverse, cells specific for a given antigen display a distinct subset of phenotypes, which differs depending on the antigen specificity and the nature of the antigen. High-content single-cell phenotypic profiling of antigen-specific T cells should allow for more accurate predictions of T cell response outcomes. Application of CyTOF-based combinatorial tetramer staining, as we previously described for fluorescent labels, will extend the utility of this approach.

APA, Harvard, Vancouver, ISO, and other styles

34

Steinbeiss, S., V. M. Temperton, and G. Gleixner. "Mechanisms of soil carbon storage in experimental grasslands." Biogeosciences Discussions 4, no. 5 (October 19, 2007): 3829–62. http://dx.doi.org/10.5194/bgd-4-3829-2007.

Full text

Abstract:

Abstract. We investigated the fate of root and litter derived carbon into soil organic matter and dissolved organic matter in soil profiles, in order to explain unexpected positive effects of plant diversity on carbon storage. A time series of soil and soil solution samples was investigated at the field site of The Jena Experiment. In addition to the main biodiversity experiment with C3 plants, a C4 species (Amaranthus retroflexus L.) naturally labeled with 13C was grown on an extra plot. Changes in organic carbon concentration in soil and soil solution were combined with stable isotope measurements to follow the fate of plant carbon into the soil and soil solution. A split plot design with plant litter removal versus double litter input simulated differences in biomass input. After 2 years, the no litter and double litter treatment, respectively, showed an increase of 381 g C m−2 and 263 g C m−2 to 20 cm depth, while 71 g C m−2 and 393 g C m−2 were lost between 20 and 30 cm depth. The isotopic label in the top 5 cm indicated that 11 and 15% of soil organic carbon were derived from plant material on the no litter and the double litter treatment, respectively. Without litter, this equals the total amount of carbon newly stored in soil, whereas with double litter this corresponds to twice the amount of stored carbon. Our results indicate that litter input resulted in lower carbon storage and larger carbon losses and consequently accelerated turnover of soil organic carbon. Isotopic evidence showed that inherited soil organic carbon was replaced by fresh plant carbon near the soil surface. Our results suggest that primarily carbon released from soil organic matter, not newly introduced plant organic matter, was transported in the soil solution and contributed to the observed carbon storage in deeper horizons.

APA, Harvard, Vancouver, ISO, and other styles

35

Rustom, R., J. S. Grime, P. Maltby, H. R. Stockdale, M. Critchley, and J. M. Bone. "Observations on the early renal uptake and later tubular metabolism of radiolabelled aprotinin (Trasylol) in man: theoretical and practical considerations." Clinical Science 84, no. 2 (February 1, 1993): 231–35. http://dx.doi.org/10.1042/cs0840231.

Full text

Abstract:

1. The novel method recently developed to measure renal tubular degradation of filtered proteins in man using radiolabelled aprotinin (Trasylol) has been modified to allow the fate and the significance of the renal catabolism of radiolabelled aprotinin to be determined beyond 24 h. 2. Ten renal patients with normal kidney function and variable proteinuria each received two separate intravenous injections of radiolabelled aprotinin, 5.0 mg of 99mTc-labelled aprotinin (40 MBq) and 0.5 mg of 131I-labelled aprotinin (5 MBq). Chromatography (Sephadex-G-25-M) was used to separate undegraded radiolabelled aprotinin from the free isotope in urine and plasma. Renal uptake from σ-camera images (24 h for 99mTc-Iabelled aprotinin and up to 96 h for 131I-labelled aprotinin) and urinary activity (48 and 96 h, respectively) were measured. 3. The renal handling of radiolabelled aprotinin was similar with the two isotopes. Chromatography showed that all plasma activity was undegraded radiolabelled aprotinin, and urine activity was only the free isotopic label. 4. Kidney uptake of 131I-labelled aprotinin was prompt, reaching a cumulative maximum of 37.1 ± 3.0% of dose at 24 h, but falling exponentially thereafter to 5.6 ± 1.0% of dose at 96 h. 5. The rate of excretion of the free label in urine, i.e. the metabolic rate of radiolabelled aprotinin, was relatively constant over the first 24 h (1.6 ± 0.09% of dose/h), but then fell in parallel with the diminishing activity over the kidney, i.e. to 1.0 ± 0.1% of dose/h over 24–48 h and to only 0.4 ± 0.08% of dose/h over 72–96 h. 6. Fractional renal degradation of radiolabelled aprotinin, derived from the mean rate of urinary excretion of the free isotope over a given interval divided by the mean cumulative kidney uptake over the same interval (h−1), fell steeply early and then more slowly to 0.05 ± 0.003 h−1 at 14.25h, and stabilized thereafter varying little between 0.04 ± 0.01 h−1 and 0.05 ± 0.01 h−1 over 36–84 h. 7. Thus, the maximum cumulative kidney uptake of radiolabelled aprotinin is achieved by 24 h, when the metabolic rate and fractional degradation are reliable indices of catabolism. The falling metabolic rate after 24 h, together with the constant rate of fractional degradation, suggests that there is a readily saturable step in the metabolic process. Hence, duplicate measurements of radiolabelled aprotinin uptake and metabolism around 24 h only (12–36 h) are sufficient and offer a simple and a reliable tool in clinical studies for determining the link between renal tubular protein degradation and renal disease progression.

APA, Harvard, Vancouver, ISO, and other styles

36

London, Robert E., and Thomas E. Walker. "Biosynthesis of trehalose by Brevibacterium flavum: Use of long range13C-13C coupling data to characterize triose phosphate isomerase activity." Bioscience Reports 5, no. 6 (June 1, 1985): 509–15. http://dx.doi.org/10.1007/bf01116950.

Full text

Abstract:

The13C isotopic labeling pattern in the disaccharide trehalose (1,1-α-α-D-glucose) produced by the micro-organismBrevibacterium flavum when grown on a medium containing [1-{au13}C]glucose has been determined. Long range coupling between C-1 and C-6 carbons of the glucose units can be observed in the excreted material. It is proposed that some of the13C isotopomers in the excreted trehalose reflect the labeling pattern in (unobserved) fructose 1,6-diphosphate. Analysis of the label distribution within the framework of a steady state kinetic model allows an analysis of the contributions of the hexose monophosphate shunt and the degree of equilibration of triose phosphate isomerase. Analogous measurements on excreted glucose could be carried out in other organisms.

APA, Harvard, Vancouver, ISO, and other styles

37

Lee, Choi Chuck, and Charles Y. Fiakpui. "Some isotopic scrambling studies with singly or doubly labeled triphenylvinyl bromide." Canadian Journal of Chemistry 63, no. 3 (March 1, 1985): 681–84. http://dx.doi.org/10.1139/v85-112.

Full text

Abstract:

The solvolysis of triphenyl[2-14C]vinyl bromide (1-Br-2-14C) in 70% HOAc – 30% H2O or in 2,2,2-trifluoroethanol (TFE) carried out in the presence of an excess of p-CH3C6H4SNa gave the triphenylvinyl p-tolyl thioether (1-STol) with a greatly decreased extent of scrambling of the 14C-label from C-2 to C-1 when compared with analogous reactions without the presence of the p-toluenethiolate anion. For example, the 1-STol product from the reaction of 1-Br-2-14C in 70% HOAc – p-CH3C6H4SNa showed only 0.5–0.9% scrambling, while previous studies on the reaction of 1-Br-2-14C in 70% HOAc – NaOAc gave 14.7 ± 0.7% scrambling. Previous work on the solvolysis of 1,2-diphenyl-2-[2H5]phenyl[2-13C]vinyl bromide (1-Br-2-13C-2-Ph-d5 in 70% HOAc, as well as the present results from the solvolysis of 1-Br-2-13C-2-Ph-d5 in TFE – 2,6-lutidine, gave products derived from all 4 possible isotopomeric triphenylvinyi cations 3, 4, 5, and 6 arising from successive 1,2-phenyl shifts. On the other hand, solvolysis of 1-Br-2-13C-2-Ph-d5 in 70% HOAc or TFE containing an excess of p-CH3C6H4SNa gave 1-STol in which the isotopically rearranged product was derived only from ion 5 arising from a 1,2-shift of the unlabeled phenyl group with no detectable amount of production derived from a 1,2-shift of the perdeuterophenyl group. These results are interpreted by the rapid trapping of the triphenylvinyi cation by the highly nucleophilic p-toluenethiolate anion.

APA, Harvard, Vancouver, ISO, and other styles

38

Che, Fa-Yun, Quan Yuan, Elena Kalinina, and Lloyd D. Fricker. "Examination of the rate of peptide biosynthesis in neuroendocrine cell lines using a stable isotopic label and mass spectrometry." Journal of Neurochemistry 90, no. 3 (August 2004): 585–94. http://dx.doi.org/10.1111/j.1471-4159.2004.02522.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Kastenmayer, Peter, Lena Davidsson, Pilar Galanz, Françise Cherouvrier, Serge Hercberg, and Richard F. Hurrell. "A double stable isotope technique for measuring iron absorption in infants." British Journal of Nutrition 71, no. 3 (March 1994): 411–24. http://dx.doi.org/10.1079/bjn19940148.

Full text

Abstract:

A stable isotope technique has been developed which uses 57Fe and 58Fe as labels and which enables the simultaneous measurement of Fe absorption from two test meals in infants. The method was evaluated by measuring Fe absorption from a commercial whey-adjusted infant formula in nine healthy infants aged 13–25 weeks. Each infant was fed 210 ml formula, labelled with either 57Fe or 58Fe, on four consecutive mornings, in random order. The total Fe content in each feed was 2.5 mg Fe; either as 2.5 mg 57Fe, or 0 6 mg 58Fe plus 1.9 mg Fe with normal isotopic composition. Isotopic enrichment of Fe in erythrocytes was measured by thermal ionization mass spectrometry 14 d after the last administration, and Fe absorption was calculated based on isotope ratio shifts, total circulating Fe and intake of each isotope. Geometric mean absorption for the 57Fe and 58Fe labels was 6.72 and 658% respectively, and the absorption of the two isotopes was not significantly different (Student's paired t test). By this technique, paired comparisons of Fe absorption can be obtained and systematic studies of the influence of dietary factors on Fe absorption during infancy can he conducted.

APA, Harvard, Vancouver, ISO, and other styles

40

van Hall, Gerrit. "Correction factors for 13C-labelled substrate oxidation at whole-body and muscle level." Proceedings of the Nutrition Society 58, no. 4 (November 1999): 979–86. http://dx.doi.org/10.1017/s0029665199001299.

Full text

Abstract:

The oxidation of fatty acids, carbohydrates and amino acids can be measured by quantifying the rate of excretion of labelled CO2 following administration of 14C- or 13C-labelled substrates at whole-body and tissue level. However, there is a theoretical need to correct the oxidation rates for the proportion of labelled CO2 that is produced via oxidation but not excreted. Furthermore, depending on the substrate and position of the C label(s), there may also be a need to correct for labelled C from the metabolized substrate that does not appear as CO2, but rather becomes temporarily fixed in other metabolites. The bicarbonate correction factor is used to correct for the labelled CO2 not excreted. Recently, an acetate correction factor has been proposed for the simultaneous correction of CO2 not excreted and label fixed in other metabolites via isotopic exchange reactions, mainly in the tricarboxylic acid cycle. Changes in metabolic rate induced, for example, by feeding, hormonal changes and physical activity, as well as infusion time, have been shown to affect both correction factors. The present paper explains the theoretical and physiological basis of these correction factors and makes recommendations as to how these correction factors should be used in various physiological conditions.

APA, Harvard, Vancouver, ISO, and other styles

41

Khosravi, M. J., and E. P. Diamandis. "Immunofluorometry of choriogonadotropin by time-resolved fluorescence spectroscopy, with a new europium chelate as label." Clinical Chemistry 33, no. 11 (November 1, 1987): 1994–99. http://dx.doi.org/10.1093/clinchem/33.11.1994.

Full text

Abstract:

Abstract We describe a new "sandwich"-type non-isotopic immunoassay for human choriogonadotropin (hCG) in serum. In the assay, hCG is captured by a beta-subunit-specific monoclonal antibody, which is immobilized in a white microtiter well. The sandwich is completed by adding a second biotinylated monoclonal antibody specific for the whole hCG molecule. The degree of binding of biotinylated antibody, which is proportional to the amount of hCG present in the sample, is quantified by adding streptavidin labeled with the europium chelate 4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid (BCPDA), in the presence of excess Eu3+. The fluorescent complex formed on the solid-phase [monoclonal antibody-hCG-monoclonal antibody-biotin-streptavidin-BCPDA-Eu3+] is measured by excitation at 337.1 nm with a nitrogen laser and monitoring the emission at 615 nm in a specially designed gated fluorometer working in a time-resolved mode. A two-step procedure is proposed for routine use to avoid the "high-dose hook effect" of the simpler and faster one-step procedure. The hCG assay described has a dynamic range of 1 to 500 int. units/L, and is precise and accurate. Results agree well with those obtained with a commercially available immunoradiometric and a time-resolved immunofluorometric procedure.

APA, Harvard, Vancouver, ISO, and other styles

42

Fonteh, A. N., and F. H. Chilton. "Rapid remodeling of arachidonate from phosphatidylcholine to phosphatidylethanolamine pools during mast cell activation." Journal of Immunology 148, no. 6 (March 15, 1992): 1784–91. http://dx.doi.org/10.4049/jimmunol.148.6.1784.

Full text

Abstract:

Abstract The objective of the present study was to better understand the remodeling of arachidonic acid (AA) in phospholipids of the mouse bone marrow-derived mast cell (BMMC) during Ag and ionophore A23187 activation. Initial studies were designed to understand the movement of AA in phospholipid classes under resting conditions. BMMC pulse labeled with AA incorporated greater than 95% of the label into the major phospholipid classes. Phosphatidylcholine (PC) subclasses, 1-acyl-2-arachidonoyl-(sn-glycero-3-phosphocholine (GPC)) in particular, initially accounted for most of the label incorporated into the cells with phosphatidylinositol/phosphatidylserine (PI/PS) and phosphatidylethanolamine (PE) subclasses containing much smaller quantities. Prolonged incubation of labeled BMMC resulted in a decrease in the radioactivity in PC with a concomitant increase in PE such that 1-alk-1-enyl-2-arachidonoyl-(sn-glycero-3-phosphoethanolamine (GPE)) became the single largest labeled AA pool by 24 h. Further experiments indicated that 24 h was the time required to reach isotopic equilibrium among AA-containing phospholipids of the BMMC. In the next series of experiments, BMMC phospholipids were labeled to different specific activities by either labeling the cells for 0.5 h or for 24 h followed by stimulation. Under isotopic equilibrium conditions (24 h), stimulation resulted in AA release from PE greater than PC much greater than PI/PS with 1-alk-1-enyl-2-arachidonoyl-GPE providing the bulk of AA released from the BMMC. By contrast, cells labeled for 0.5 h released AA from PC much greater than PI/PS, with 1-acyl-2-arachidonoyl-GPC accounting for most of the AA released from BMMC phospholipids. Label associated with PE subclasses under nonequilibrium conditions remained unchanged or slightly increased throughout a 10-min stimulation period. Finally, BMMC were double labeled with [14C]-AA for 24 h and then with [3H]-AA for 0.5 h. Cell stimulation resulted in a decrease in the [3H]/[14C] ratio in PC and PI and an increase in the ratio in PE. The decrease in [3H]/[14C] ratio in PC was mainly in 1-acyl-2-arachidonoyl-GPC, whereas the increase in PE subclasses was primarily in 1-alk-1-enyl-2-arachidonoyl-GPE. The [3H]/[14C] ratio in cellular neutral lipids and in supernatant fluid products were at values between PC and PE subclasses. Taken together, these data suggest that during Ag activation, the release of free arachidonic acid is from predominantly PE subclasses. Concomitant with the release of AA, there is a rapid remodeling of AA from PC subclasses into PE subclasses (1-alk-1-enyl-2-acyl-GPE).

APA, Harvard, Vancouver, ISO, and other styles

43

Simons, Brigitte L., Guanghui Wang, Rong-Fong Shen, and Mark A. Knepper. "In vacuo isotope coded alkylation technique (IVICAT); an N-terminal stable isotopic label for quantitative liquid chromatography/mass spectrometry proteomics." Rapid Communications in Mass Spectrometry 20, no. 16 (2006): 2463–77. http://dx.doi.org/10.1002/rcm.2615.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Serdyuk, I. N., and G. Zaccaï. "Triple Isotopic Substitution Method in Small-Angle Neutron Scattering: Application to Some Problems of Structural Biology." Journal of Applied Crystallography 30, no. 5 (October 1, 1997): 787–91. http://dx.doi.org/10.1107/s0021889897002872.

Full text

Abstract:

The triple isotopic substitution (TIS) method is based on the analysis of a scattering curve which is the difference between the scattering of two solutions containing appropriately deuterium-labelled particles. A necessary condition for the application of the method is that the two solutions are identical in all respects except for the extent of the deuterium label. Such an experimental scheme has allowed a number of unique physical experiments to be performed, the main ones being: (1) elimination of the contribution of the interparticle interference; (2) addition of both small- and large-sized foreign particles to those studied without distortions of the structural data; (3) highlighting of individual (quite small) regions in the molecules; (4) suppression of the dimerization contribution to the scattering curve. The application of this method is of special interest for studying the mutual three-dimensional disposition of individual small regions of molecules (3D mapping) and for investigating the geometrical properties of the surfaces of globular proteins. It is evident that TIS has a wide range of experimental possibilities, demonstrating that small-angle neutron scattering is one of the most informative structural methods for low resolution.

APA, Harvard, Vancouver, ISO, and other styles

45

Lemos, Paulo C., Luísa S. Serafim, Margarida M. Santos, Maria A. M. Reis, and Helena Santos. "Metabolic Pathway for Propionate Utilization by Phosphorus-Accumulating Organisms in Activated Sludge: 13C Labeling and In Vivo Nuclear Magnetic Resonance." Applied and Environmental Microbiology 69, no. 1 (January 2003): 241–51. http://dx.doi.org/10.1128/aem.69.1.241-251.2003.

Full text

Abstract:

ABSTRACT In vivo 13C and 31P nuclear magnetic resonance techniques were used to study propionate metabolism by activated sludge in enhanced biological phosphorus removal systems. The fate of label supplied in [3-13C]propionate was monitored in living cells subjected to anaerobic/aerobic cycles. During the anaerobic phase, propionate was converted to polyhydroxyalkanoates (PHA) with the following monomer composition: hydroxyvalerate, 74.2%; hydroxymethylvalerate, 16.9%; hydroxymethylbutyrate, 8.6%; and hydroxybutyrate, 0.3%. The isotopic enrichment in the different carbon atoms of hydroxyvalerate (HV) produced during the first anaerobic stage was determined: HV5, 59%; HV4, 5.0%; HV3, 1.1%; HV2, 3.5%; and HV1, 2.8%. A large proportion of the supplied label ended up on carbon C-5 of HV, directly derived from the pool of propionyl-coenzyme A (CoA), which is primarily labeled on C-3; useful information on the nature of operating metabolic pathways was provided by the extent of labeling on C-1, C-2, and C-4. The labeling pattern on C-1 and C-2 was explained by the conversion of propionyl-CoA to acetyl-CoA via succinyl-CoA and the left branch of the tricarboxylic acid cycle, which involves scrambling of label between the inner carbons of succinate. This constitutes solid evidence for the operation of succinate dehydrogenase under anaerobic conditions. The labeling in HV4 is explained by backflux from succinate to propionyl-CoA. The involvement of glycogen in the metabolism of propionate was also demonstrated; moreover, it was shown that the acetyl moiety to the synthesis of PHA was derived preferentially from glycogen. According to the proposed metabolic scheme, the decarboxylation of pyruvate is coupled to the production of hydrogen, and the missing reducing equivalents should be derived from a source other than glycogen metabolism.

APA, Harvard, Vancouver, ISO, and other styles

46

Yang, Jehoon, Su Xu, and Jun Shen. "Fast Isotopic Exchange between Mitochondria and Cytosol in Brain Revealed by Relayed 13C Magnetization Transfer Spectroscopy." Journal of Cerebral Blood Flow & Metabolism 29, no. 4 (January 21, 2009): 661–69. http://dx.doi.org/10.1038/jcbfm.2008.170.

Full text

Abstract:

In vivo13C magnetic resonance spectroscopy has been applied to studying brain metabolic processes by measuring 13C label incorporation into cytosolic pools such as glutamate and aspartate. However, the rate of exchange between mitochondrial α-ketoglutarate/oxaloacetate and cytosolic glutamate/aspartate ( Vx) extracted from metabolic modeling has been controversial. Because brain fumarase is exclusively located in the mitochondria, and mitochondrial fumarate is connected to cytosolic aspartate through a chain of fast exchange reactions, it is possible to directly measure Vx from the four-carbon side of the tricarboxylic acid cycle by magnetization transfer. In isoflurane-anesthetized adult rat brain, a relayed 13C magnetization transfer effect on cytosolic aspartate C2 at 53.2ppm was detected after extensive signal averaging with fumarate C2 at 136.1ppm irradiated using selective radiofrequency pulses. Quantitative analysis using Bloch–McConnell equations and a four-site exchange model found that VxE13–19 µmol per g per min (≫ VTCA, the tricarboxylic acid cycle rate) when the longitudinal relaxation time of malate C2 was assumed to be within ±33% of that of aspartate C2. If VxE VTCA, the isotopic exchange between mitochondria and cytosol would be too slow on the time scale of 13C longitudinal relaxation to cause a detectable magnetization transfer effect.

APA, Harvard, Vancouver, ISO, and other styles

47

Shen, Jun, Douglas L. Rothman, Kevin L. Behar, and Su Xu. "Determination of the Glutamate—Glutamine Cycling Flux Using Two-Compartment Dynamic Metabolic Modeling is Sensitive to Astroglial Dilution." Journal of Cerebral Blood Flow & Metabolism 29, no. 1 (September 3, 2008): 108–18. http://dx.doi.org/10.1038/jcbfm.2008.102.

Full text

Abstract:

Over the last decade 13C magnetic resonance spectroscopy (13C MRS) combined with the infusion of [1-13C]glucose has been used to measure the cerebral rate of the glutamate—glutamine cycle ( Vcyc). However, the effect of the astroglial label dilution pathways on the accuracy and precision of the C MRS measurement of Vcyc has not been evaluated or realized. In this report, we use the numerical Monte Carlo method to study the effect of astroglial dilution on the reliability of extracting Vcyc using the neuronal-astroglial two-compartment metabolic model and [1-13C]glucose infusion. The results show that omission of the astroglial dilution flux leads to a large loss in the sensitivity of the glutamine turnover curve to Vcyc. When the measured isotopic dilution of cerebral glutamine is accounted for in the analysis, the value of Vcyc can be precisely and accurately determined.

APA, Harvard, Vancouver, ISO, and other styles

48

Murphy, D. V., I. R. P. Fillery, and G. P. Sparling. "Method to label soil cores with 15NH3 gas as a prerequisite for 15N isotopic dilution and measurement of gross N mineralization." Soil Biology and Biochemistry 29, no. 11-12 (November 1997): 1731–41. http://dx.doi.org/10.1016/s0038-0717(97)00067-9.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

van der Meer, Marcel T. J., Stefan Schouten, Mary M. Bateson, Ulrich Nübel, Andrea Wieland, Michael Kühl, Jan W. de Leeuw, Jaap S. Sinninghe Damsté, and David M. Ward. "Diel Variations in Carbon Metabolism by Green Nonsulfur-Like Bacteria in Alkaline Siliceous Hot Spring Microbial Mats from Yellowstone National Park." Applied and Environmental Microbiology 71, no. 7 (July 2005): 3978–86. http://dx.doi.org/10.1128/aem.71.7.3978-3986.2005.

Full text

Abstract:

ABSTRACT Green nonsulfur-like bacteria (GNSLB) in hot spring microbial mats are thought to be mainly photoheterotrophic, using cyanobacterial metabolites as carbon sources. However, the stable carbon isotopic composition of typical Chloroflexus and Roseiflexus lipids suggests photoautotrophic metabolism of GNSLB. One possible explanation for this apparent discrepancy might be that GNSLB fix inorganic carbon only during certain times of the day. In order to study temporal variability in carbon metabolism by GNSLB, labeling experiments with [13C]bicarbonate, [14C]bicarbonate, and [13C]acetate were performed during different times of the day. [14C]bicarbonate labeling indicated that during the morning, incorporation of label was light dependent and that both cyanobacteria and GNSLB were involved in bicarbonate uptake. 13C-labeling experiments indicated that during the morning, GNSLB incorporated labeled bicarbonate at least to the same degree as cyanobacteria. The incorporation of [13C]bicarbonate into specific lipids could be stimulated by the addition of sulfide or hydrogen, which both were present in the morning photic zone. The results suggest that GNSLB have the potential for photoautotrophic metabolism during low-light periods. In high-light periods, inorganic carbon was incorporated primarily into Cyanobacteria-specific lipids. The results of a pulse-labeling experiment were consistent with overnight transfer of label to GNSLB, which could be interrupted by the addition of unlabeled acetate and glycolate. In addition, we observed direct incorporation of [13C]acetate into GNSLB lipids in the morning. This suggests that GNSLB also have a potential for photoheterotrophy in situ.

APA, Harvard, Vancouver, ISO, and other styles

50

DiNuzzo, Mauro. "Kinetic Analysis of Glycogen Turnover: Relevance to Human Brain 13C-NMR Spectroscopy." Journal of Cerebral Blood Flow & Metabolism 33, no. 10 (June 12, 2013): 1540–48. http://dx.doi.org/10.1038/jcbfm.2013.98.

Full text

Abstract:

A biophysical model of the glycogen molecule is developed, which takes into account the points of attack of synthase and phosphorylase at the level of the individual glucose chain. Under the sole assumption of steric effects governing enzyme accessibility to glucosyl residues, the model reproduces the known equilibrium structure of cellular glycogen at steady state. In particular, experimental data are reproduced assuming that synthase (1) operates preferentially on inner chains of the molecule and (2) exhibits a faster mobility than phosphorylase in translocating from an attacked chain to another. The model is then used to examine the turnover of outer versus inner tiers during the labeling process of isotopic enrichment (IE) experiments. Simulated data are fitted to in vivo13C nuclear magnetic resonance spectroscopy measurements obtained in the human brain under resting conditions. Within this experimental set-up, analysis of simulated label incorporation and retention shows that 7% to 35% of labeled glucose is lost from the rapidly turning-over surface of the glycogen molecule when stimulation onset is delayed by 7 to 11.5 hours after the end of [1-13C]glucose infusion as done in actual procedures. The substantial label washout before stimulation suggests that much of the subsequent activation-induced glycogenolysis could remain undetected. Overall, these results show that the molecular structure significantly affects the patterns of synthesis and degradation of glycogen, which is relevant for appropriate design of labeling experiments aiming at investigating the functional roles of this glucose reserve.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Isotopic label'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles