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Biomedical subjects

G Navon

Publications and source records attributed to G Navon.

At least 91 records · Page 5Linked to original sources
PubMed1987

Acute pancreatitis in rats: a 31P nuclear magnetic resonance study.

High resolution 31P nuclear magnetic resonance (NMR) was used to evaluate the severity of acute pancreatitis in rats. Experimental pancreatitis was induced by intraparenchymal injection of 10% sodium taurocholate. pancreases were removed at various time periods and the NMR spectrum of the whole organ was recorded. Metabolic changes taking place during the progression of the disease were measured and correlated with the pathologic changes. Gradual depletion of the high energy compounds, adenosine triphosphate and phosphocreatine, was observed. The NMR spectral changes paralleled the extension of the pathologic lesions and were found to constitute a reliable indicator of the severity of acute pancreatitis. It is suggested that high resolution NMR may be used to evaluate the pathogenesis and therapy of various forms of experimental pancreatitis.

Adenosine Triphosphate↗
PubMed1987

The protective effect of enriched branched chain amino acid formulation in the ischemic heart: a phosphorous-31 nuclear magnetic resonance study.

Branched chain amino acids (BCAA) have been found to have a protective effect on the ischemic myocardium. Isolated rat hearts were perfused with phosphate-free Krebs-Henseleit (KH) solution with or without BCAA. A Latex balloon-tipped catheter was inserted into the left ventricle to measure intracavitary pressures. Hearts were subjected to 18 minutes of 'no flow' global ischemia and then reperfused for 30 mins at 37 degrees C. Metabolism of high energy phosphates during ischemia and recovery was studied by P-31 NMR. Intracellular pH was calculated from the chemical shift of Pi. Pressure recovery was better with KH + BCAA (89 +/- 16%) than with KH (41 +/- 26%) (P = 0.0001); dP/dt recovery was also improved with BCAA (84 +/- 19% vs 27 +/- 27% for KH) (P = 0.0003). After 18 mins of ischemia, ATP levels in the BCAA group were higher than in the KH perfused hearts (33 +/- 20 vs 17 +/- 10% of pre-ischemic value) (P = 0.02). No significant difference was found in the intracellular pH at the end of the ischemic period. Following reperfusion the recovery of pH was better in the BCAA group (7.09 +/- 0.06 vs 7.04 +/- 0.06) (P = 0.03). These results show that BCAA protect the heart from myocardial ischemic injury, decrease depletion of ATP during ischemia, and enhance post-ischemic hemodynamic function.

Adenosine Triphosphate↗
PubMed1987

P NMR Study of Elicitor Treated Phaseolus vulgaris Cell Suspension Cultures.

The addition of an elicitor (glucan) to Phaseolus vulgaris cell suspension cultures increased the formation of the phytoalexin phaseollin. Intracellular pH and phosphate concentrations were studied with (31)P nuclear magnetic resonance spectroscopy on elicitor-treated cells which were aerated during the nuclear magnetic resonance measurement. The pH of the vacuole and to a lesser extent the pH of the cytoplasm were affected at 10 minutes after elicitor addition; a decrease in pH from 5.3 to 4.8 was noted in the vacuole and from 7.46 to 7.28 in the cytoplasm. The ratio between the amount of Pi in the vacuole to that in the cytoplasm also changed within 10 minutes after elicitor addition. The signal for ATP (beta-ATP) was low after elicitor addition and was high again 23 hours after elicitation. Forty-eight hours after elicitor addition, vacuolar and cytoplasmic pH had almost returned to their initial values. The rapid change in vacuolar and cytoplasmic pH may cause the change of metabolism that occurs in elicitor-treated P. vulgaris cells.

Journal Article↗
PubMed1986

Liposomes containing paramagnetic macromolecules as MRI contrast agents.

The use of paramagnetic ions, bound to macromolecules and trapped in liposomes, as MRI contrast agents is suggested. As an example, the system of Mn2+ bound to serum proteins was tested. The binding of the metal ions to the macromolecules enhances their relaxation and at the same time decreases their rate of diffusion out of the liposomes. The use of liposomes is expected to reduce the potential toxicity of the paramagnetic ions and allows their targeting toward specific tissues.

Beta-Globulins↗
PubMed1986

Sodium-23 NMR relaxation times in body fluids.

23Na longitudinal and transverse NMR relaxation times were measured in human serum, plasma, cerebrospinal fluid (CSF), and solutions of plasma proteins. The magnetization decay curves could not be resolved into two exponentials. A procedure to extract quantitative information from the measured relaxation rates in such a case was developed. The relaxation times of 23Na in serum and plasma were analyzed in terms of the different contributions from free Na+, Na+ bound to small molecules, and Na+ bound to various protein fractions in these body fluids. While T1 is essentially that of free Na+ in a solution which is slightly more viscous than salt solution, T2 is influenced by binding to proteins with the largest contribution from serum albumin. The effect of binding to small molecules on T1 and T2 is negligible. From measurements of the relaxation times at several magnetic field strengths a rotational correlation time of Na+ bound to serum albumin of 16 +/- 6 ns was obtained. The fraction of bound Na+ in serum and plasma was roughly estimated as 0.02% of the total sodium. The relaxation times in cerebrospinal fluid are very similar to those of NaCl solution.

Blood↗
PubMed1985

The determination of intracellular water space by NMR.

A new method for the determination of intracellular water space using NMR spectroscopy is described. The method is based on the measurement of 59Co NMR signal intensity of an inert, stable and membrane-impermeable cobalt(III) compound such as Co(CN)3-6 or Co(imidazole)3+6 and the 2H or 1H NMR signal intensities of the freely permeable water. As an example of the method, the variation of the intracellular water space of human erythrocytes as a function of osmolality was measured.

Cobalt Radioisotopes↗
PubMed1985

Phosphorus-31 and proton NMR analysis of reproductive organs of male rats.

Phorphorus NMR spectra of the whole reproductive organs of male rats and their perchloric acid extracts indicate the presence of phosphocholine and phosphoethanolamine in the testis, glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) in the epididymis, and creatine phosphate, GPC, and GPE in the seminal vesicles. High amounts of carnitine and inositol were observed by the proton NMR of perchloric acid extract of the corpus and cauda epididymis. Smaller amounts of these compounds were observed in the caput epididymis and vas deferens; they were totally absent in the testis. Creatine is present in high concentrations in the testis, vas deferens, and seminal vesicles. It is almost absent in all parts of the epididymis.

Animals↗
PubMed1984

NMR relaxation studies of intracellular Na+ in red blood cells.

The state of intracellular Na+ in human and dog erythrocytes was characterized by 23Na-NMR using dysprosium complexes as shift reagents. Intracellular Na+ concentrations were determined using integration of the inner Na+ NMR signals and measurements of the intracellular volume using 59Co-NMR of extracellular Co(CN)3-6. T2 was found to be significantly shorter than T1, indicating some binding to macromolecules. While the longitudinal magnetization decay follows a single exponential, the transverse magnetization could be fitted with a double-exponential function. It was shown that neither the binding to the inner side of the membrane nor binding to hemoglobin contributes to the relaxation enhancement.

Animals↗
PubMed1984

1H and 31P nuclear magnetic resonance spectroscopy of erythrocyte extracts in myotonic muscular dystrophy.

Extracts freshly prepared from erythrocytes of patients with myotonic muscular dystrophy, their unaffected siblings, and normal control subjects were examined with both 1H and 31P nuclear magnetic resonance spectroscopy. A moderate variability was found in the relative amounts of various nonphosphorylated compounds among patients and control subjects; however, no significant differences were found between the groups. As for the phosphorylated compounds, the sum of ADP + ATP was found significantly elevated in the myotonic muscular dystrophy patients.

Adolescent↗
PubMed1983

Differences in metabolite levels upon differentiation of intact neuroblastoma X glioma cells observed by proton NMR spectroscopy.

Proton NMR spectroscopy was used to study the effect of differentiation with prostaglandin E1 and theophylline on intact hybrid neuroblastoma X glioma cells. The standard proton NMR method showed more resolvable signals than the spin echo NMR spectra. The differentiated cells were found to contain significantly higher levels of glutamine than the undifferentiated precursors. Observations on cell extracts confirmed these results.

Animals↗
PubMed1982

Studies of the conformation of bilirubin and its dimethyl ester in dimethyl sulphoxide solutions by nuclear magnetic resonance.

The conformation of bilirubin and its dimethyl ester in dimethyl sulphoxide (DMSO) was investigated by n.m.r. spectroscopy. The chemical shifts of the pyrrole NH and Lactam protons of bilirubin and its dimethyl ester in DMSO indicate a strong interaction with the solvent. Inter-proton distances were calculated from nuclear Overhauser effects (NOE), selective and non-selective relaxation times (T1) and rotational correlation times taken from 13C relaxation times. The interproton distances indicate that the conformation of the skeleton of bilirubin and its dimethyl ester in DMSO is similar to that of bilirubin and mesobilirubin in the crystalline state and in chloroform solutions, except for a possible slight twist of the pyrrolenone rings about the methine bonds, which may be a consequence of solvation of the NH groups by DMSO. Unlike in chloroform solutions, no direct hydrogen-bonding occurs between the carboxylic acid and the lactam groups of bilirubin in DMSO, as shown by the absence of an NOE between these groups. The fast exchange of the pyrrole NH protons with 2H shows that no hydrogen-bonding occurs between these protons and the propionic residues, in line with their solvation by DMSO. From the above results, and from the slowness of the internal motion of the propionic residues of bilirubin and its dimethyl ester, it is concluded that these residues are tied to the skeleton via bound solvent molecules.

Bilirubin↗
PubMed1980

Nuclear magnetic resonance studies of carbonic anhydrase catalyzed reversible hydration of acetaldehyde by the saturation transfer method.

The catalysis of the chemical exchange between acetaldehyde and its hydrate by bovine carbonic anhydrase B was investigated by the NMR line broadening and saturation transfer techniques. While both chemical exchange and binding to the enzyme had an effect on the line broadening of acetaldehyde and its hydrate, the saturation transfer method enabled us to measure the exchange without the interference from the effect of the binding. p-Toluenesulfonamide and azide ion were found to inhibit completely the carbonic anhydrase catalyzed exchange reaction. However, there was a residual line broadening of the acetaldehyde by the enzyme in their presence. This was interpreted as binding to sites other than the active site of the enzyme. The pH profile of the catalysis of the reversible hydration of acetaldehyde by carbonic anhydrase in the absence of a buffer indicates high- and low-activity forms of the enzyme with a transition at pD 7.65. The cadmium(II) enzyme was found to be inactive, and the cobalt(II) derivative was found to have similar activity to that of the native system.

Acetaldehyde↗
PubMed1979

Phosphorus-31 nuclear magnetic resonance studies of wild-type and glycolytic pathway mutants of Saccharomyces cerevisiae.

High-resolution phosphorus-31 nuclear magnetic resonance (31P NMR) spectra of wild-type and mutant strains of Saccharomyces cerevisiae were observed at a frequency of 145.7 MHz. Levels of various phosphorus metabolites were investigated upon addition of glucose under both aerobic and anaerobic conditions. Three mutant strains were isolated and their biochemical defects characterized: pfk lacked phosphofructokinase activity; pgi lacked phosphoglucose isomerase activity; and cif had no glucose catabolite repression of the fructose bisphosphatase activity. Each mutant strain was found to accumulate characteristic sugar phosphates when glucose was added to the cell suspension. In the case of the phosphofructokinase deficient mutant, the appearance of a pentose shunt metabolite was observed. 31P NMR peak assignments were made by a pH titration of the acid extract of the cells. Separate signals for terminal, penultimate, and central phosphorus atoms in intracellular polyphosphates allowed the estimation of their average molecular weight. Signals for glycero(3)phosphochline, glycero(3)phosphoserine, and glycero(3) phosphoethanolamine as well as three types of nucleotide diphosphate sugars could be observed. The intracellular pH in resting and anaerobic cells was in the range 6.5--6.8 and the level of adenosine 5'-triphosphate (ATP) low. Upon introduction of oxygen, the ATP level increased considerably and the intracellular pH reached a value of pH 7.2--7.3, irrespective of the external medium pH, indicating active proton transport in these cells. A new peak representing the inorganic phosphate of one of the cellular organelles, whose pH differed from the cytoplasmic pH, could be detected under appropriate conditions.

Adenosine Triphosphate↗
PubMed1979

Kinetic and magnetic properties of cobalt(III) ion in the active site of carbonic anhydrase.

Cobalt(III)bovine carbonic anhydrase B was prepared by the oxidation of the cobalt(II) enzyme with hydrogen peroxide and was purified by affinity chromatography. The oxidation reaction is inhibited by specific inhibitors of carbonic anhydrase. The inhibition is explained by the fact that the Co(II)-enzyme . inhibitor complex cannot be directly oxidized by hydrogen peroxide, but has to dissociate to give free Co(II) enzyme which is then oxidized. The Co(III) ion in Co(III) carbonic anhydrase cannot be directly substituted by zinc ions. It can be reduced by either dithionite or BH-4 ions to give, first, their complexes with the Co(II) enzyme, and upon their removal, a fully active Co(II) enzyme. Cyanide and azide bind to cobalt(III) carbonic anhydrase with similar rate constants of 0.060 +/- 0.005 and 0.070 +/- 0.007 M-1 S-1 respectively. These rates are faster than those found for Co(III) inorganic complexes. The Co(III) ion in both Co(III) carbonic anhydrase and Co(III) carboxypeptidase A was found to be diamagnetic, indicating a near octahedral symmetry.

Animals↗
PubMed1978

On the measurement of pH in Escherichia coli by 31P nuclear magnetic resonance.

The 31P high resolution NMR spectra of concentrated suspensions of Escherichia coli cells have been measured at 145.8 MHz. The position of the orthophosphate resonance is used as a measure of internal and external pH. In accord with Paddan, Zilberstein and Rottenberg ((1976) Eur. J. Biochem. 63, 533--541) it is shown that when properly energized the internal pH is 7.5 +/- 0.1. By synchronizing the NMR data acquisition with 3-s bursts of O2 it is possible to measure the internal pH with a time resolution of about 1 s. It is shown that at 20 degrees C the pH remains constant for times longer than 15 s after the oxygen is discontinued and it decays in several minutes.

Escherichia coli↗
PubMed1978

Phosphate metabolites in lymphoid, Friend erythroleukemia, and HeLa cells observed by high-resolution 31P nuclear magnetic resonance.

High-resolution phosphorus-31 nuclear magnetic resonance spectra were observed for cell lines from mammalian sources: lymphoid cells, Friend erythroleukemia cells, and HeLa cells. Some phosphate metabolites were identified and their concentrations were found to vary among the different cell lines. ATP/ADP ratios could be measured in the living cells. The phospholipid metabolites phosphorylcholine and phosphorylethanolamine and their glyceryl esters were present in relatively high concentrations in the cells, but their ratios varied considerably. Also, a high concentration of an unidentified diphosphodiester compound was observed in the Friend erythroleukemia and HeLa cells. No appreciable pH gradient across the cell membrance was observed in these three mammalian cell lines, in contrast to the large pH gradient detected in microorganisms.

Adenosine Diphosphate↗