| 1. |
- McIntyre, Deane D., et al.
(författare)
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Nitrogen-14 NMR relaxation, and reorientation behavior of dissolved dinitrogen
- 1989
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856 .- 0022-2364. ; 83:2, s. 377-382
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, nitrogen- 14 and - 15 NMR spectroscopy has become an important technique in organic chemistry and in biochemistry ( Z-4). A frequent occurrence in the NMR spectra of both nuclei is the presence of a signal at approximately -7 1.5ppm (referred to neat nitromethane; -66 ppm referred to aqueous nitrate). This resonance, which has been observed in water (4) and a range of organic solvents (.5-7), has been the subject of some confusion in the literature. In the case of nitrogen-14 NMR spectra, the signal for the quadrupolar nucleus has a remarkably narrow linewidth (about 25 Hz) compared to those recorded for a wide variety of other substances. This indicates a fairly high degree of electronic symmetry about the nitrogenatom and/or a very short correlation time ( 7,). In a recent report (8)) this signal has been assigned to dissolved dinitrogen on the basis that it could be removed by degassing´the solution; however, no reference was made to the fact that it had a remarkably narrow linewidth compared to other 14N NMR resonances. When detected in the 15NCIDNP spectra of the decomposition products of diazonium ions (5, 6) as well as azo compounds ( 7)) the signal has been assigned either to dinitrogen (6, 7) or to a terminal diazonium nitrogen (5). This work is in general agreement with our own observations over a period of years which indicate that the signal arises from dissolved dinitrogen. We have measured the 14N chemical shift of dissolved N2 in a number of solvents at 25°C and have also determined the T, and T2 relaxation times under a variety of conditions in solvents of different viscosity. This Note is concerned with a discussion of these 14N NMR observations and with the determination of the correlation time of dissolved dinitrogen which permits the determination of both the enthalpy and the entropy of activation via the Eyring equation. These results will be compared with earlier reported data regarding the chemical shift and relaxation of liquid nitrogen obtained under a variety of conditions ( 9-12). All spectra were obtained on a Bruker AM-400 wide-bore NMR spectrometer operating in the FT mode at a frequency of 28.9 MHz for 14N and 40.5 MHz for 15N, using a 10 mm broadband probe. Typical conditions for the acquisition of 14N spectra
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| 2. |
- Brodelius, Peter, et al.
(författare)
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A Phosphorus-31 Nuclear Magnetic Resonance Study of Phosphate Uptake and Storage in Cultured Catharanthus roseus and Daucus carota Plant Cells
- 1985
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 260, s. 3556-3560
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Tidskriftsartikel (refereegranskat)abstract
- High resolution "P NMR spectra (103.2 MHz) ofoxygenated Catharanthus roseu8 and Daucus carotacells grown in suspension cultures were obtained usinga solenoidal perfusion probe. The spectra showed resonancesfor various phosphorylated metabolites suchas ATP, ADP, NAD(P)(H), nucleoside diphosphoglucose,and sugar phosphates. The relative levels ofthe phosphorylated metabolites remained constantthroughout the growth curve. No resonances for storagecompounds such as polyphosphates, pyrophosphate,or phytates were observed. Two resolved resonancesfor Pi indicated an intracellular pH of 7.3 and5.7 (or below) for the cytoplasm and vacuoles, respectively.The time course of Pi uptake and storage duringgrowth in fresh culture medium was followed by studyingthe level of vacuolar Pi with 31PN MR (145.7 MHz).Simultaneously, the level of Pi in the culture mediumwas followed with radioactive s2P. C. roseus quicklytakes up all the Pi from the culture medium (maximumrate 1.7 pmol min" g" (dry weight of cells)). The Pi isfirst stored in the vacuoles; subsequently, one part ofthis pool is used to keep a constant cytoplasmic Pi levelwhile another part is apparently accumulated as anNMR invisible Pi store, probably in another cell organelle.In contrast, D. carota does not accumulate Pi inthe vacuoles and consequently it takes up Pi from themedium at a much slower rate (0.05 pmol min" g"(dry weight of cells)).
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| 3. |
- Hellstrand, Per, et al.
(författare)
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Phosphagens and intracellular pH in intact rabbit smooth muscle studied by 31P-NMR
- 1985
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Ingår i: American Journal of Physiology: Cell Physiology. - 1522-1563. ; 248:3 Pt 1, s. 320-329
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus-31 nuclear magnetic resonance (NMR) spectra (103.2 MHz) were obtained from rabbit portal vein, urinary bladder, and taenia coli smooth muscle. The muscles were mounted isometrically as strips in a horizontal probe and superfused with oxygenated medium at 23 degrees C. Under these conditions the preparations could remain in a stable metabolic state for at least 24 h. The resonances observed represented phosphocreatine (PC), adenosine triphosphate (ATP), and phosphomonoester. The PC-ATP ratio in relaxed preparations was approximately 1.9 (bladder) and 1.4 (taenia coli), approximately consistent with chemical analysis of tissue extracts by isotachophoresis. However, the levels of adenosine diphosphate (ADP) and inorganic phosphate (Pi) were considerably lower as estimated by NMR, suggesting intracellular compartmentalization. Contraction for 30 min in high-K+ medium caused a reversible 10-30% decline of PC but no change in ATP. Intracellular pH was 7.0 +/- 0.1 and was unchanged by contraction or inhibition of tissue respiration by cyanide. Treatment with 2-deoxyglucose resulted in accumulation of 2-deoxyglucose 6-phosphate, verifying the pH assignment. However, the phosphomonoester resonance of normal spectra is not glucose 6-phosphate. Treatment with Mg2+-free, high-Mg2+ (10 mM), or hyperosmotic media did not alter the Mg2+ saturation of ATP. The results obtained by the nontissue-destructive 31P-NMR measurements are consistent with the view that metabolic steady-state conditions are maintained during contraction in the smooth muscle.
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| 4. |
- Lundberg, Peter, et al.
(författare)
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A35Cl--NMR study of the singular anion-binding properties of dromedary hemoglobin
- 1989
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434. ; 999:1, s. 12-8
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Tidskriftsartikel (refereegranskat)abstract
- 35Cl(-)-NMR measurements of chloride binding to carbonmonoxy- and deoxy-dromedary hemoglobin reveal the existence of two classes of chloride-binding sites, one of high and the other of low affinity. Although this situation resembles that described for human hemoglobin, it was found that the number of binding sites as well as the association equilibrium constant for chloride binding are significantly higher in the dromedary protein. This difference may be due to the greater number of basic residues exposed to solvent and to the higher flexibility of dromedary hemoglobin. The two oxygen-linked polyanion-binding sites characteristic of this hemoglobin show competition for some of the high-affinity chloride-binding sites in keeping with their location in the cleft enclosed by the beta chains and between the alpha chains termini. It is suggested that the observed anion-binding properties of dromedary hemoglobin may contribute to the control of the physiological osmotic shock after rehydration.
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| 5. |
- Lundberg, Peter, et al.
(författare)
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Carbon-13 and proton NMR studies of post-mortem metabolism in bovine muscles
- 1986
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Ingår i: Meat Science. - : Elsevier. - 0309-1740 .- 1873-4138. ; 18:2, s. 133-160
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Tidskriftsartikel (refereegranskat)abstract
- Proton and carbon-13 NMR was used to investigate post-mortem metabolism in bovine muscles at 26°C during the first 10h after slaughter. WALTZ-16 decoupling was used to eliminate the proton couplings in the (13)C spectra and the 'jump and return' pulse sequence was used to suppress the water resonance in the (1)H-NMR experiments. With carbon-13 NMR the glycogen breakdown and the lactate development could be followed. This was compared with the lactate, creatine and phosphocreatine development as measured by proton NMR. The intracellular pH was estimated from the chemical shift of the abundant dipeptide, carnosine, as measured in the (1)H- and (13)C-NMR spectra. These were compared with similar measurements obtained earlier using phosphorus-31 NMR. The three independently determined pH profiles were in excellent agreement with one another, as well as with results obtained with the standard iodoacetate extraction method. In the course of these studies we observed that the post-mortem metabolism in cow and heifer was slow and that it took four more hours to complete compared to bull or young bull. After 10 h the pH was 5·9 in bull and 6·1 in cow. Phosphocreatine had completely disappeared after 3·5 h in bull samples while the lactate continued to increase even after 10h. The curves obtained by carbon-13 and proton NMR for the increase in lactate during the first 10 h post mortem were very similar. Moreover, plots for the increase in the lactate level versus the intracellular pH decrease showed a linear relationship, indicating that anaerobic glycolytic activity is the main determining cause for the intracellular pH decrease. Various other parameters, such as the ratio of unsatirated to saturated fatty acid side chains and the presence of amino acids and taurine, could be measured from the in vivo carbon-13 NMR spectra. However, no gross changes occured in any of these parameters during the first 10 h post mortem.
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| 6. |
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| 7. |
- Lundberg, Peter, et al.
(författare)
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NMR as a Noninvasive Tool in Meat Research
- 1987
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Ingår i: Annals of the New York Academy of Sciences. - : John Wiley & Sons. - 0077-8923 .- 1749-6632. ; 508, s. 516-522
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Tidskriftsartikel (refereegranskat)abstract
- NMR has been used for some time for in vivo measurements of biological tissues and has established itself as a valuable and complementary method to be used in parallel with traditional extraction methods. To date most attention has been paid to problems such as central biochemical pathways, energy metabolism in simple organisms and organs, and of course to problems encountered in medicine. There has been relative little interest in applying NMR to problems in food technology, even if these questions can have a tremendous impact on everyday life. Following a suggestion by Gadian,' we show here that multinuclear metabolic NMR is a useful method for studying post-mortem events in carcasses of slaughtered animals.The treatment and storage of carcasses during the first hours after slaughter is of extreme importance for the final quality and tenderness of the meat. Mistreatment can cause large economical losses and waste of valuable food. For example, in order to reduce the risk of bacterial infections one would like to cool down a carcass as soon as possible. Nevertheless, if a muscle is cooled down below 15OC before the postmortem metabolism is completed it may shorten dramatically thus decreasing the tenderness of the meat.' Therefore it is important to measure the rates of postmortem metabolism and to study the efficiency of methods that are aimed at speeding up this process.
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| 8. |
- Lundberg, Peter, et al.
(författare)
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Permeabilization of Plant Cells: 31P NMR Studies of the Permeability of the Tonoplast
- 1986
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Ingår i: Plant Cell Reports. - : Springer. - 0721-7714 .- 1432-203X. ; 5, s. 13-16
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Tidskriftsartikel (refereegranskat)abstract
- A suspension culture of Catharanthus roseus has been used to study the permeability of cell membranes after treatment with various concentrations of a permeabilizing agent (DMSO). The uptake and release (after permeabilization) of inorganic phosphate (Pi) by cells have been investigated by 32P radiotracer and non-invasive phosphorus-31 NMR experiments. These studies have demonstrated that measurements of the Pi-efflux from plant cells provide a reliable measure of the permeability of the tonoplast.
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| 9. |
- Lundberg, Peter, et al.
(författare)
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Phosphorus-31 and Nitrogen- 14 NMR Studies of the Uptake of Phosphorus and Nitrogen Compounds in the Marine Macroalgae Ulva lactuca
- 1989
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 89:4, s. 1380-1387
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Tidskriftsartikel (refereegranskat)abstract
- Cytoplasmic phosphomonoesters and inorganic phosphate, as well as vacuolar inorganic phosphate and polyphosphates, gave rise to the major peaks in (31)P nuclear magnetic resonance (NMR) spectra of the marine macroalgae Enteromorpha sp., Ceramium sp., and Ulva lactuca which were collected from the sea. In contrast, NMR-visible polyphosphates were lacking in Pylaiella sp. and intracellular vacuolar phosphate seemed to act as the main phosphorus store in this organism. In laboratory experiments, polyphosphates decreased in growing U. lactuca which was cultivated in continuous light under phosphate-deficient conditions. In contrast, the same organism cultivated in seawater with added phosphate and ammonium, accumulated phosphate mainly in the form of polyphosphates. When nitrate was provided as the only nitrogen source, accumulation of polyphosphates in the algae decreased with increasing external nitrate concentration. From the chemical shift of the cytoplasmic Pi peak, the cytoplasmic pH of superfused preparations of Ulva was estimated at 7.2. The vacuolar pH, determined from the chemical shifts of the vacuolar Pi and the terminal polyphosphate peaks, was between 5.5 and 6.0. The intracellular nitrate and ammonium levels in U. lactuca were determined by (14)N NMR. Both nitrogen sources were taken up and stored intracellularly; however, the uptake of ammonium was much faster than that of nitrate.
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| 10. |
- Lundberg, Peter, et al.
(författare)
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Post-mortem metabolism in fresh porcine, ovine and frozen bovine muscle
- 1987
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Ingår i: Meat Science. - : Elsevier. - 0309-1740 .- 1873-4138. ; 19:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Post-mortem metabolism was followed by phosphorus-31-NMR in muscle samples obtained from freshly slaughtered pigs and lambs. Resonances for creatine phosphate (CP), ATP, inorganic phosphate (Pi) and sugar phosphates (SP) could be discerned and the intracellular pH could be determined from the spectra. The rates of post-mortem metabolism varied in the following fashion: porcine muscle > ovine muscle > bovine muscle. However, the course of post-mortem metabolism was, in all cases, the same. CP disappeared first and then ATP. Simultaneously, Pi increased, while SP remained relatively constant. The intracellular pH decreased to pH 5·5 in all tissues.In a separate set of experiments the post-mortem metabolism during thawing was studied in bovine muscles that had been frozen immediately after slaughter. Again, the same course of post-mortem metabolism was observed, but the thaw shortening was accompanied by an extremely rapid post-mortem metabolism, which was more than ten times as fast as that measured for fresh bovine muscles. The intracellular pH decreased from 7·2 to 5·5 in 45 min. This rapid metabolism started only after the sample ha reached 0°C. Resonances for metabolites were broadened in frozen muscles due to the limited motions that are allowed within the ice lattice.
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