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S B Petersen

Publications and source records attributed to S B Petersen.

At least 55 records · Page 3Linked to original sources
PubMed1993

Metabolism of [U-13C]glutamate in astrocytes studied by 13C NMR spectroscopy: incorporation of more label into lactate than into glutamine demonstrates the importance of the tricarboxylic acid cycle.

Primary cultures of cerebral cortical astrocytes were incubated with [U-13C]glutamate (0.5 mM) in modified Dulbecco's medium for 2 h. Perchloric acid (PCA) extracts of the cells as well as redissolved lyophilized media were subjected to NMR spectroscopy to identify 13C-labeled metabolites. NMR spectra of the PCA extracts exhibited distinct multiplets for glutamate, aspartate, glutamine, and malate. The culture medium showed peaks for a multitude of compounds released from the astrocytes, among which lactate, glutamine, alanine, and citrate were readily identifiable. For the first time incorporation of label into lactate from glutamate was clearly demonstrated by doublet formation in the C-3 position and two doublets in the C-2 position of lactate. This labeling pattern can only occur by incorporation from glutamate, because natural abundance will only produce singlets in proton-decoupled 13C spectra. Glutamine, released into the medium, was labeled uniformly to a large extent, but the C-3 position not only showed the expected apparent triplet but also a doublet due to 13C incorporation into the C-4 position of glutamine. The doublet accounted for 11% of the total label in the glutamine synthesized and released within the incubation period. The corresponding labeling pattern of [13C]glutamate in the PCA extracts showed that 19% of the glutamate contained 12C. Labeling of lactate, citrate, malate, and aspartate as well as incorporation of 12C into uniformly labeled glutamate and glutamine could only arise via the tricarboxylic acid cycle. The relative amount of glutamate metabolized via this route is at least 70% as calculated from the areas of the C-3 resonances of these compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

NMR spectroscopic studies of 13C acetate and 13C glucose metabolism in neocortical astrocytes: evidence for mitochondrial heterogeneity.

Neocortical astrocytes were incubated with 13C-labeled substrates to determine metabolic pathways. 13C NMR spectroscopy was used to analyze 13C incorporation into glutamine and citrate from the different precursors--[1-13C]glucose or [2-13C]acetate. When glucose was the labeling substrate, incorporation due to pyruvate carboxylation should be observed in the C-2 position in glutamine and the C-4 position in citrate. A large incorporation due to pyruvate carboxylation was observed in glutamine in the C-2 and C-3 positions, but not in citrate. When acetate was the precursor, the labeling ratios in the C-2/C-4 positions in glutamine and in the equivalent positions in citrate were 0.27 and 0.11, respectively. Moreover, acetate labeled lactate in the C-2 position much less than did glucose. Altogether, these observations led to the conclusion that glutamine precursors and citrate are either produced in different types of astrocytes or in different tricarboxylic acid cycles, situated in functionally different mitochondria in the same cell, and that in all likelihood pyruvate carboxylase is expressed differently in these mitochondria.

Acetates↗
PubMed1993

Glutamate and glutamine metabolism and compartmentation in astrocytes.

Metabolism of glutamate and glutamine in cultured mouse cerebral cortical astrocytes has been investigated using either radioactively labelled (14C) amino acids or 13C-labelled amino acids combined with NMR spectroscopy of cell extracts and lyophilyzed incubation media. Using [U-13C]glutamate it has been shown that in astrocytes exogenously supplied glutamate is primarily (70%) metabolized oxidatively through the tricarboxylic acid (TCA) cycle and to a lesser extent (30%) directly to glutamine. Glutamate metabolized in the TCA cycle is to a large extent recovered as lactate showing that the astrocyte-specific enzyme, malic enzyme is functionally active. Incubation with [U-14C]glutamine led to a higher specific radioactivity in glutamate than in glutamine. It could also be shown that glutamate and glutamine were metabolized differently to aspartate and alanine. These results taken together strongly suggest that glutamate/glutamine metabolism in astrocytes is compartmentalized and a model with multiple cytoplasmic and mitochondrial compartments of these amino acids is proposed.

Animals↗
PubMed1993

Utilization of glutamine and of TCA cycle constituents as precursors for transmitter glutamate and GABA.

In the present review evidence is presented that (1) glutamine synthesis in astrocytes is essential for synthesis of GABA in neurons; (2) alpha-ketoglutarate in the presence of alanine (as an amino group donor) can replace glutamine as a precursor for synthesis of transmitter glutamate, but maybe not as a precursor for transmitter GABA; (3) differences exist in the intraneuronal metabolic pathways for utilization of alpha-ketoglutarate plus alanine and of glutamine, and (4) alanine also functions as a substrate for oxidative metabolism in glutamatergic neurons. It should be emphasized that the supply of precursors for transmitter glutamate and GABA in glutamatergic and GABAergic neurons depends on metabolic processes in astrocytes regardless whether glutamine or alpha-ketoglutarate plus L-alanine function as the transmitter precursors. The key reason that an interaction with astrocytes is essential is that both pyruvate carboxylase, the major enzyme in the brain for net synthesis of tricarboxylic acid cycle intermediates, and glutamine synthetase, the enzyme forming glutamine from glutamate, are specifically located in astrocytes, but not in neurons.

Animals↗
PubMed1992

1H NMR study of cortex neurons and cerebellar granule cells on microcarriers and their PCA extracts: lactate production under hypoxia.

Lactate production of 6-day-old cerebral cortex neurons and 7-day-old cerebellar granule cells from mouse brain attached to cytodex 3 microcarriers was studied as a function of time, under hypoxic conditions using 1H NMR. Perchloric acid extracts of both cell types were prepared and 1H NMR spectra showed compounds characteristic for these neurons. In particular the granule cell extracts showed a large amount of glutamate as expected from biochemical experiments, whereas the cortex neurons showed a large amount of 4-aminobutyric acid.

Animals↗
PubMed1992

Contrast-enhanced magnetic resonance imaging of the breast.

Contrast-enhanced magnetic resonance imaging (MRI) of 28 patients with known breast tumors was compared with clinical findings and histopathology, and for 12 of the patients also with mammography. The dynamic measurements performed in 18 patients showed that signal intensity in gradient echo (FFE) images increased rapidly in malignant tumors after contrast injection and reached a plateau level at 1-3 min postcontrast. Fibroadenomas showed slower contrast enhancement continuing throughout the whole examination period of 10 min. The most enhancing parts of the tumors were selected for intensity measurements. The differentiation between malignant and benign tumors in dynamic contrast-enhanced MRI was in accordance with the histopathological findings in all cases. The tumor diameter as measured by MRI showed very good agreement with the size of the tumor specimens. Comparison of tumor size measurements in mammography and MRI showed that MRI had the most accurate correlation to the measured size of the tumor specimens.

Adenocarcinoma, Mucinous↗
PubMed1991

First direct demonstration of preferential release of citrate from astrocytes using [13C]NMR spectroscopy of cultured neurons and astrocytes.

Primary cultures of cerebral cortical neurons or astrocytes or the two cell types together (co-cultures) were incubated with [1-13C]glucose for 20 or 48 h. Subsequently, perchloric acid (PCA) extracts of the cells as well as redissolved lyophilized media were subjected to NMR spectroscopy in order to detect 13C-labeled amino acids (glutamine, glutamate, gamma-aminobutyrate (GABA)) and other metabolites (lactate, tricarboxylic acid cycle (TCA) constituents). NMR spectra of PCA extracts of neurons or co-cultures exhibited distinct peaks for glutamate and GABA whereas the PCA extracts of astrocytes and co-cultures showed peaks corresponding to glutamine and glutamate. This pattern is consistent with the neuronal location of the GABA synthesizing enzyme glutamate decarboxylase and the astrocytic localization of the glutamine synthesizing enzyme, glutamine synthetase. NMR spectra of the incubation media showed clearly that 13C-labeled citrate, alanine and glutamine were synthesized and released from astrocytes since only media from the astrocyte cultures or co-cultures or neurons and astrocytes contained these metabolites in detectable amounts. It may be concluded that astrocytes play an important role supplying neurons with precursors for biosynthesis of glutamate and GABA such as glutamine and TCA cycle constituents. Since among the latter only citrate could be found in significant amounts it may be hypothesized that this may be the quantitatively most important TCA constituent to be released from astrocytes and subsequently utilized by neurons.

Animals↗
PubMed1991

Characterization of microcarrier cultures of neurons and astrocytes from cerebral cortex and cerebellum.

In the present investigation a method is described for culturing cerebellar granule cells (glutamatergic neurons), cerebral cortical neurons (GABAergic neurons) and cortical astrocytes on Cytodex 3 microcarriers. It was possible to obtain a high yield of attached neurons and astrocytes on the microcarriers and the cell specific characteristics such as the ability to release neurotransmitter (neurons) and a high activity of glutamine synthetase (astrocytes) were preserved. This system, allowing mixtures of neurons and astrocytes at any given ratio to be produced, may constitute an attractive model system by which the interaction between neurons and astrocytes with regard to exchange of neurotransmitter precursors as well as other compounds may be studied.

Aging↗
PubMed1990

Calcium binding in alpha-amylases: an X-ray diffraction study at 2.1-A resolution of two enzymes from Aspergillus.

X-ray diffraction analysis (at 2.1-A resolution) of an acid alpha-amylase from Aspergillus niger allowed a detailed description of the stereochemistry of the calcium-binding sites. The primary site (which is essential in maintaining proper folding around the active site) contains a tightly bound Ca2+ with an unusually high number of eight ligands (O delta 1 and O delta 2 of Asp175, O delta of Asn121, main-chain carbonyl oxygens of Glu162 and Glu210, and three water molecules). A secondary binding site was identified at the bottom of the substrate binding cleft; it involves the residues presumed to play a catalytic role (Asp206 and Glu230). This explains the inhibitory effect of calcium observed at higher concentrations. Neutral Aspergillus oryzae (TAKA) alpha-amylase was also refined in a new crystal at 2.1-A resolution. The structure of this homologous (over 80%) enzyme and additional kinetic studies support all the structural conclusions regarding both calcium-binding sites.

Amino Acid Sequence↗
PubMed1990

Analysis of the secondary structure of the human immunodeficiency virus (HIV) proteins p17, gp120, and gp41 by computer modeling based on neural network methods.

A neural network computer program, trained to predict secondary structure of proteins by exposing it to matching sets of primary and secondary structures from a database, was used to analyze the human immunodeficiency virus (HIV) proteins p17, gp120, and gp41 from their amino acid sequences. The results are compared to those obtained by the Chou-Fasman analysis. Two alpha-helical sequences corresponding to the putative fusigenic domain and to the transmembrane domain of gp41 could be predicted, as well as a possible binding site between p17 and gp41. On the basis of the secondary structure predictions, a three-dimensional model of p17 was constructed. This model was found to represent a stable conformation by an analysis using an energy-minimization program. The model predicts that p17 is attached to the membrane only by the acylated N-terminus, in analogy with the N-terminus of the gag protein of other retroviruses and also with the src oncogene protein p60src. The intracellular C-terminal part of gp41 may act as a receptor by electrostatic interaction with p17.

Algorithms↗
PubMed1988

Protein secondary structure and homology by neural networks. The alpha-helices in rhodopsin.

Neural networks provide a basis for semiempirical studies of pattern matching between the primary and secondary structures of proteins. Networks of the perceptron class have been trained to classify the amino-acid residues into two categories for each of three types of secondary feature: alpha-helix or not, beta-sheet or not, and random coil or not. The explicit prediction for the helices in rhodopsin is compared with both electron microscopy results and those of the Chou-Fasman method. A new measure of homology between proteins is provided by the network approach, which thereby leads to quantification of the differences between the primary structures of proteins.

Amino Acid Sequence↗
PubMed1984

[NMR imaging of fluorine-containing substances. 19-Fluorine ventilation and perfusion studies].

Physiologically inert perfluorinated gases may be used for lung ventilation imaging by Nuclear Magnetic Resonance (NMR). Because the nuclear concentration in the gas is lower than in tissue, signals from large gas volumes must be integrated to produce an acceptable image quality. After a series of phantom studies, preliminary dog studies have been carried out, using breathable mixtures of CF4 and O2. The resulting images have been compared with Xe ventilation scans. Furthermore, perfluorinated solutions were imaged using phantoms. The results are described and the future potential of the technique discussed.

Animals↗
PubMed1983

[NMR-whole body tomography: a new imaging method].

NMR tomography (zeugmatography) can provide 2D and true 3D images of the human body. Advantages of this new imaging method in medicine are the possibilities to get both anatomic and functional images at one time without any invasive procedures. Furthermore, NMR has no ionizing radiation hazards. The spacial resolution of NMR tomography ranges between 0.5 and 3.0 mm. Within the next years, NMR tomography will replace several conventional X-ray, CAT scanning and nuclear medicine techniques. This article gives a brief survey of NMR basics and its medical applications.

Abdominal Neoplasms↗
PubMed1983

[NMR whole-body tomography. Requirements for equipment and space].

First general considerations of the new NMR technique are given. Then disturbing influences on the magnet coming from outside as well as influences upon the environs coming from the magnet are pointed out. Next the inside arrangements of examination rooms are discussed. Finally accessory and emergency equipment for the examination rooms are mentioned.

Computers↗
PubMed1983

Aspects of cardiac diagnosis using synchronized NMR imaging.

In vivo synchronized 3D Proton NMR zeugmatographic images of the beating heart have been obtained. The images clearly show the cardiac anatomy and changes in the anatomy accompanying the cardiac cycle. Transverse, coronal and sagittal slices are presented.

Animals↗
PubMed1979

Visual impairment: facing possible blindness.

Blindness real or threatened often constitutes a major crisis for the eye patient. This paper discusses the use of crisis intervention during the acute phase of medical care to support the coping patterns of the patient and his family and prepare them for the rehabilitation tasks ahead.

Adaptation, Psychological↗