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M Brauer

Publications and source records attributed to M Brauer.

At least 73 records · Page 4Linked to original sources
PubMed1991

Transgenic tobacco plants expressing yeast-derived invertase in either the cytosol, vacuole or apoplast: a powerful tool for studying sucrose metabolism and sink/source interactions.

In higher plants sucrose plays a central roles with respect to both short-term storage and distribution of photoassimilates formed in the leaf. Sucrose is synthesized in the cytosol, transiently stored in the vacuole and exported via the apoplast. In order to elucidate the role of the different compartments with respect to sucrose metabolism, a yeast-derived invertase was directed into the cytosol and vacuole of transgenic tobacco plants. This was in addition to the targeting of yeast-derived invertase into the apoplast described previously. Vacuolar targeting was achieved by fusing an N-terminal portion (146 amino acids long) of the vacuolar protein patatin to the coding region of the mature invertase protein. Transgenic tobacco plants expressing the yeast-derived invertase in different subcellular compartments displayed dramatic phenotypic differences when compared to wild-type plants. All transgenic plants showed stunted growth accompanied by reduced root formation. Starch and soluble sugars accumulated in leaves indicating that the distribution of sucrose was impaired in all cases. Expression of cytosolic yeast invertase resulted in the accumulation of starch and soluble sugars in both very young (sink) and older (source) leaves. The leaves were curved, indicating a more rapid cell expansion or cell division at the upper side of the leaf. Light-green sectors with reduced photosynthetic activity were evenly distributed over the leaf surface. With the apoplastic and vacuolar invertase, the phenotypical changes induced only appear in older (source) leaves. The development of bleached and/or necrotic sectors was linked to the source state of a leaf. Bleaching followed the sink to source transition, starting at the rim of the leaf and moving to the base. The bleaching was paralleled by the inhibition of photosynthesis.

Base Sequence↗
PubMed1991

Indoor exposures to fine aerosols and acid gases.

Indoor exposures to aerosols and gases are associated with both indoor and outdoor air pollution sources. The identification of sources and the assessment of their relative contribution can be a complicated process due to a) the presence of numerous indoor sources, which can vary from building to building; b) the uncertainties associated with the estimation of the impact of outdoor sources on indoor air quality; c) the interactions between pollutants; and d) the importance of reactions between pollutants and indoor surfaces. It is well established that fine particles (diameter less than or equal to 2.5 microns) originating from outdoor sources such as automobiles, oil and coal combustion, incineration, and diverse industrial activities can penetrate into the indoor environment. Indoor/outdoor ratios, usually varying between 0.4 and 0.8, depend on parameters such as particle size and density, air exchange rate, and the surface-to-volume ratio of the indoor environment. Determining fine particle elemental composition makes it possible to identify the contribution of different outdoor sources. This paper focuses on the origin and the concentration of indoor aerosols and acid gases by highlighting the results from two indoor air quality studies.

Aerosols↗
PubMed1991

1H NMR analyses of methyl group-containing metabolites in rat liver extracts--effects of starvation, anoxia, acute glycerol and carbon tetrachloride treatment and chronic ethanol administration on hepatic metabolism.

400 MHz 1H NMR spectroscopy was used to analyze methyl group-containing metabolites in perchloric acid extracts of livers of rats treated with carbon tetrachloride or fed with ethanol-containing liquid diets, and sacrificed with carbon dioxide anoxic euthanasia or pentobarbital euthanasia (with or without 12-18 hour fasting). In all cases, coenzyme A was detected using 1H NMR spectroscopy, but at higher levels for chronic ethanol-treated rats. Propionate was also detected in livers 6 hours after treatment with carbon tetrachloride. The assignments of the 1H NMR resonances in a spectrum of biological origin to these two metabolites have not been previously reported. Another unusual metabolite, 1,2-propanediol, was also observed in dramatically elevated levels in starved rats. The methyl groups for coenzyme A, propionate, and 1,2-propanediol have 1H NMR chemical shifts at 0.73 and 0.87 ppm, 1.18 ppm, and 1.14 ppm (from tetramethylsilane) respectively. In addition to the above mentioned resonances, glutamine, glutamate, proline, acetate, leucine, alanine, lactate, ethanol, beta-hydroxybutyrate, and valine were also observed in the 0.5-2.3 ppm methyl region of the 1H NMR spectra. Biochemical changes were also observed in these latter metabolites. beta-Hydroxybutyrate was increased by chronic ethanol administration; this increase was exacerbated by starvation. Alanine was decreased by chronic ethanol administration. Acetate was increased by chronic ethanol administration except when glycerol was added to the liver or when the rat was starved. We also observed an unassigned triplet at 0.81 ppm, and its appearance seems to be correlated with that of 1,2-propanediol.

Amino Acids↗
PubMed1990

In vitro 31P-NMR spectroscopic studies of rat liver subjected to chronic ethanol administration.

31P-NMR spectroscopy of rat liver perchloric acid extracts was utilized to assess hepatic levels of major phosphorylated metabolites with and without ethanol administration from 0 to 51 days. The results are: (1) 3-phosphoglycerate was largely decreased starting from the first day of ethanol ingestion, (2) in ethanol-treated rats, phosphoethanolamine exhibited a significant decrease relative to the control rats until around day 30, (3) glycerophosphocholine and glycerophosphoethanolamine decreased over the entire period of ethanol ingestion, (4) ATP, AMP, Pi and energy charge showed significant changes due to ethanol effects when a 40-50 s exposure to CO2 was used prior to freeze-clamping, but ADP did not change, and (5) the other observable metabolites did not show statistically significant change. Some time-dependent changes in metabolite concentration, although not dramatic, were observed from day 1 to day 51 of ethanol administration. Our results indicate that chronic ethanol ingestion results in an inhibition of glycolysis and gluconeogenesis, a decrease in phospholipid breakdown and a lowering of hepatic energy charge.

Adenosine Diphosphate↗
PubMed1990

Sodium-23 and proton nuclear magnetic resonance imaging studies of carbon tetrachloride-induced liver damage in the rat.

Magnetic resonance imaging techniques were used to investigate the response of the liver of the rat in situ to a toxicological challenge by carbon tetrachloride. Proton images were taken as transverse slices through the rat before and after intraperitoneal administration of the hepatotoxin. Two to three hours after carbon tetrachloride was given, a region of high proton signal intensity was observed where the portal vein enters the liver. Sodium-23 images were also taken, and a region of high sodium intensity was observed in the same location within the liver as the increased proton intensity. The results suggest that acute administration of carbon tetrachloride induces localized liver damage in the region where the hepatotoxin first enters the liver. This liver damage is manifest as edema with a buildup of sodium ion and water, which can be readily detected by sodium-23 and proton NMR imaging techniques, respectively.

Animals↗
PubMed1989

In vivo and in vitro 31P-NMR spectroscopy of rat liver treated with halocarbons.

Both in vivo and in vitro 31P-NMR spectroscopy were used to demonstrate metabolic changes in rat liver as a function of time after exposure to either carbon tetrachloride (CCl4) or bromotrichloromethane (BrCCl3). The inorganic phosphate resonance, measured in vivo, moves upfield, which is associated with a decrease in cytosolic pH over a 12 or 20 h period (for BrCCl3 or CCl4, respectively). Intoxication by CCl4 or BrCCl3 causes an intracellular acidosis to pH 7.05 or 6.82 (+/- 0.05), respectively. Also, it has been found that halocarbon exposure increases the amounts of phosphomonoesters (PME) detected. High resolution in vitro 31P-NMR spectroscopy studies of perchloric acid extracts of CCl4-treated rat livers indicated a significant increase in the height of the phosphocholine resonance in the PME region 4-5 h after CCl4 exposure.

Adenine Nucleotides↗
PubMed1989

In vivo proton nuclear magnetic resonance imaging and spectroscopy studies of halocarbon-induced liver damage.

Proton magnetic resonance imaging and localized NMR spectroscopy were used to study the rat liver in situ. Respiratory gating was used in both the imaging and the localized spectroscopy studies to control for the movement of the upper abdomen of the rat during breathing. After administration of carbon tetrachloride, bromotrichloromethane, or halothane, localized regions of high proton signal intensity were observed in the NMR images of the liver. Localized (VOSY) proton NMR spectra from within these regions indicated that the increase in a signal intensity was due to a longer T2 relaxation time for the water resonance, indicating acute edema in the region of tissue damage.

Administration, Inhalation↗
PubMed1988

Factors influencing the formation of the carbon dioxide radical anion (.CO2-) spin adduct of PBN in the rat liver metabolism of halocarbons.

Spin trapping techniques have been used to detect free radicals generated from the in vitro metabolism by rat liver microsomes of carbon tetrachloride (CCl4) and bromotrichloromethane (BrCCl3) under conditions of varying oxygen tension and pH. Dispersions of rat liver microsomes incubated with 12CCl4, 13CCl4 or Br12CCl3, alpha-phenyl-tert-butyl nitrone (PBN) and NADPH/NADH in a phosphate buffer varying in pH from 6.6 to 8.0 under varying oxygen tensions produced various amounts of four different PBN adducts: PBN-CCl3, PBN-L, PBN-OL and PBN-CO2- where L is a carbon-centered lipid type radical and LO is an oxygen-centered lipid type radical. The relative amount of PBN-CO2- increases with the absence of oxygen. With the use of 31P-NMR in vivo spectroscopy it was possible to detect a pH change from 7.4 to 6.8 in the livers of rats treated with CCl4 or BrCCl3. These results suggest that halocarbon metabolism in biological systems may depend on both oxygen tension as well as pH.

Animals↗
PubMed1986

19F nuclear magnetic resonance studies of selectively fluorinated derivatives of G- and F-actin.

G-Actin is a globular protein (Mr 42 300) known to have three cysteine residues that are at least partially exposed and chemically reactive (Cys-10, -284, and -374). When G-actin was reacted with 3-bromo-1,1,1-trifluoropropanone, three resolvable 19F resonances were observed in the 19F NMR spectrum. This fluorinated G-actin derivative remained fully polymerizable, and its 31P NMR spectrum was not significantly different from that of unmodified G-actin, indicating that the chemical modification did not denature the actin and the modified residues do not interfere with the extent of polymerization or the binding of adenosine 5'-triphosphate. One of the three 19F resonances was assigned to fluorinated Cys-374 on the basis of its selective reaction with N-ethylmaleimide. This resonance was dramatically broadened after polymerization of fluorinated G-actin, while the other two resonances were not markedly broadened or shifted. Thus, Cys-10 and -284 are not involved in or appreciably affected by the polymerization of G-actin, while the mobility of the 19F label at Cys-374 is markedly reduced.

Acetone↗
PubMed1986

The cryoprotective effects of dimethyl sulfoxide on human bone marrow as studied by 31P nuclear magnetic resonance spectroscopy.

31P nuclear magnetic resonance spectroscopy has been used to study freshly aspirated normal human bone marrow samples. The pH within the intact cells of the samples was determined from the chemical-shift position of the resonance for inorganic phosphate within the cell; the intracellular pH was found to be 7.35 for fresh bone marrow. The chemical-shift positions of the alpha and beta phosphate resonances of adenosine 5'-triphosphate were used to assess the fraction of this metabolite complexed with Mg2+. It was found that 84% of the total intracellular adenosine 5'-triphosphate was in the Mg2+-complexed form. The concentration of Mg2+ uncomplexed to any ligand was 0.4 mM. The areas of the resonances for the major phosphorus-containing metabolites were used to determine intracellular concentrations. For fresh human bone marrow, the intracellular concentrations determined were phosphate monoesters less than 0.3 mM, 2,3-diphosphoglycerate 3.9 +/- 1.0 mM, inorganic phosphate 1.2 +/- 0.6 mM, phosphodiesters 2.8 +/- 1.0 mM, adenosine 5'-triphosphate 1.6 +/- 0.4 mM, adenosine 5-diphosphate less than 0.2 mM, and nicotinamide adenine dinucleotide less than 0.2 mM. These metabolite concentrations within the intact cell samples did not change over 2.0 h and changed only gradually over a 24-h period. 31P nuclear magnetic resonance spectroscopy was then used to study the cryopreservation of normal human bone marrow in the presence of increasing concentrations of the penetrating cryopreservative dimethyl sulfoxide. Dimethyl sulfoxide alone without freezing was found to cause some gradual hydrolysis of 2,3-diphosphoglycerate, presumably by stimulating diphosphoglycerate phosphatase. The effect of freezing human bone marrow to liquid nitrogen temperatures, storage, and rapid thawing was a dramatic fall in intracellular adenosine 5'-triphosphate levels. The half-life of the metabolite, after thawing, was about 0.3 h. If the bone marrow was frozen in the presence of 2.5, 5.0, and 7.5% dimethyl sulfoxide, the post-thaw half-life was prolonged to 0.4, 0.5, and 0.6 h, respectively. 15% dimethyl sulfoxide afforded complete cryoprotection, with adenosine 5'-triphosphate levels constant for 15 h after thawing the human bone marrow.

2,3-Diphosphoglycerate↗
PubMed1985

31P and 35Cl nuclear magnetic resonance measurements of anion transport in human erythrocytes.

The exchange of anions across the erythrocyte membrane has been studied using 31P nuclear magnetic resonance (NMR) to monitor inorganic phosphate influx and 35Cl NMR to monitor chloride ion efflux. The 31P NMR resonances for intracellular Pi and extracellular Pi could be observed separately by adjusting the initial extracellular pH to 6.4, while the intracellular pH was 7.3. The 35Cl NMR resonance for intracellular Cl- was so broad as to be virtually undetectable (line width greater than 200 Hz), while that of extracellular Cl-is relatively narrow (line width of about 30 Hz). The transports of Pi and Cl-were both totally inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonate, a potent inhibitor of the band 3 protein. Since the 31P resonance of Pi varies with pH, intra- and extracellular pH changes could also be determined during anion transport. The extracellular pH rose and intracellular pH fell during anion transport, consistent with the protonated monoanionic H2PO4-form of Pi being transported into the erythrocyte rather than the deprotonated dianionic HPO24-form. The rates of Cl-efflux and Pi influx were determined quantitatively and were found to be in close agreement with values determined by isotope measurements. The Cl-efflux was found to coincide with the influx of the monoanionic H2PO4-form of Pi.

Adult↗
PubMed1982

Effects of manganous ion on the phosphorus-31 nuclear magnetic resonance spectrum of adenosine triphosphate bound to nitrated G-actin: proximity of divalent metal ion and nucleotide binding sites.

G-Actin has one high-affinity binding site for ATP and one high-affinity binding site for divalent metal ions such as Ca2+, Mg2+, or Mn2+. 31P NMR has been used to study the high-affinity ATP binding site of a relatively nonpolymerizable selectively nitrated derivative of G-actin. When paramagnetic manganous ion was added to nitrated G-actin, the line widths of the resonances for the alpha-, beta-, and gamma-phosphates of the bound ATP did not increase substantially. However, the areas of the resonances of all three phosphates decreased with increasing concentration of manganous ion. This decrease in area paralleled a decrease in tightly bound calcium displaced by the manganous ion. Manganese-induced polymerization of the nitrated G-actin was found to be a relatively minor process in these experiments. The 31P NMR results are consistent with very slow exchange between the Ca2+ X ATP X nitrated G-actin complex and the Mn2+ X ATP X nitrated G-actin complex. Thus, the areas of the observed resonances, which represent the Ca2+ X ATP X nitrated G-actin complex, vary as a function of the population of this complex, but the line widths are not affected by exchange with the Mn X ATP X nitrated G-actin complex. The line widths of the 31P NMR resonances of the bound ATP in the Mn X ATP X nitrated G-actin complex are too broad to be detected (greater than 400 Hz) due to the paramagnetic effect of the tightly bound manganous ion. This indicates that the high-affinity metal ion binding site on G-actin (occupied by manganous ion) must be less than 10 A from the ATP binding site.

Actins↗
PubMed1981

Phosphorus-31 nuclear magnetic resonance studies of the adenosine 5'-triphosphate-calcium-G-actin complex.

Phosphorus-31 nuclear magnetic resonance spectra of the adenosine 5'-triphosphate-calcium-G-actin complex were obtained, and the resonances of the three phosphates of the protein-bound ATP were detected. The exchange of the ATP between its protein-bound and free states were found to be slow on the NMR time scale, with an exchange rate of less than 480 s-1 at pH* 7.8, 4 degrees C. The line width of the protein-bound gamma-phosphate resonance (corrected for spin-spin splitting by the beta phosphate) was used to calculate a rotational correlation time for the G-actin-bound ATP. With the assumption that chemical shift anisotropy is the dominant relaxation mechanism at 109.29 MHz and that the chemical shielding tensor for pyrophosphate serves as a good model for the gamma phosphate of the bound ATP, a correlation time of 60 ns was estimated. Since the theoretical correlation time of a globular protein the size of G-actin is 36 ns, the line width of the bound gamma-phosphate resonance is consistent with that expected for ATP bound to G-actin without large-scale rapid internal mobility. The addition of 1.5 M urea to the ATP-Ca-G-actin complex caused exchange broadening of the gamma and beta phosphates, but no effect on the alpha phosphate. This indicates an increase in the rate of exchange for the beta and gamma phosphates between the protein-buried and solvent-exposed environments at 1.5 M urea. At 6 M urea, the intensities of the protein-bound ATP resonances were greatly reduced, and the intensities of the free ATP resonances were greatly increased, indicative of complete protein unfolding and liberation of protein-bound ATP.

Actins↗
PubMed1980

[Sex hormones in young pigs. I. Concentrations of plasma progesterone and estrogens of sows and urinary estrogens after synchronization of estrus and ovulation].

Treatment for synchronised heat and ovulation, using Suisynchron-Prämix, Bernburg, pregnant-mare serum gonadotrophin (PMSG), and human chorionic gonadotrophin (HCG), was followed with twelve gilts by daily measurement over 31 days of urine oestrogens, plasma progesterone as well as of plasma oestrogens during the oestric phases. Hormonal developments recorded during the oestrus and luteum phases were in agreement with the concepts and data so far known for the subject. An intermediate peak of oestrogen concentration was clearly recordable in the di-oestrus, that is between the tenth and 15th days of cycle. Its physiological importance will have to be further investigated.

Animals↗
PubMed1978

1H NMR studies of the binding of EDTA to bovine pancreatic ribonuclease.

EDTA binds at the active site of ribonuclease causing a selective downfield shift of the C2 proton resonance of His 12 at pH 5.5 (pH denotes an uncorrected glass electrode pH meter reading of a 2H2O solution). A dissociation constant for EDTA binding to ribonuclease of 1.70 mM was calculated from this chemical shift change. The pKa of His 12 increased from 5.79 in ribonuclease alone to 6.73 in the RNAase . EDTA complex. Compared to these effects, the other histidine residues were not significantly affected by EDTA. EDTA was shown to act as a competitive inhibitor of cytidine 2',3'-cyclic phosphate hydrolysis by ribonuclease with a Ki of 1.37 mM at pH 5.5, 25 degrees C. Molecular model building suggests that three of the four carboxyl groups of EDTA could simultaneously interact with histidine 12, lysine 41 and lysine 7. A complex of this type would account for the data described herein.

Animals↗