bluuebunny/crossref_metadata_2025_split huggingface dataset:
MODULATORS OF GLUTAMINASE ACTIVITY
Authors: Weil‐Malherbe H. 
Published: October 2006

Abstract— The activating effect of GTP on particulate preparations of glutaminase from rat brain or rat kidney was competitively inhibited by cyclic guanosine 3′,5′‐monophosphate (c‐GMP). Similarly, the effect of ATP was inhibited by cyclic adenosine 3′,5′‐monophosphate (c‐AMP). In the absence of an added activator, the glutaminase activity of brain or kidney particles, if measurable, was also inhibited by c‐GMP and c‐AMP. GTP was a stronger activator than ATP, and c‐GMP was a stronger inhibitor than c‐AMP, for the enzyme from either tissue. The K1, of c‐GMP was about 40 mM, that of c‐AMP was about 60 mM, as determined with a brain preparation.Soluble preparations of glutaminase from pig brain and pig kidney were activated, in decreasing order of efficiency, by riboflavin phosphate, GTP, ATP and orthophosphate. The relative potencies were similar for the soluble enzymes from brain and kidney and also in the particulate and soluble forms of the brain enzyme. The apparent Km, values for the soluble brain enzyme were about the same (9–10 mM) whether riboflavin phosphate, GTP, ATP or 100 mM orthophosphate were used as activators. The Km increased with concentrations of orthophosphate lower than 100 mM, but was not significantly affected by changes in the concentrations of the other activators. Results for the kidney enzyme were similar, but the Km, tended to be somewhat lower. The estimation of the apparent KA with either the brain or kidney enzyme preparation indicated that affinities and activating efficiency were related.The activating effects of carboxylic acids on the soluble brain enzyme were similar to those on the particulate brain enzyme in terms of some correlation to the number of carboxylic groups per molecule and the potentiation by orthophosphate, but in the soluble kidney enzyme these effects were less marked or absent.
PYRUVATE METABOLISM IN THE LOBSTER NERVE AS AFFECTED BY THE PARTIAL PRESSURE OF CARBON DIOXIDE: OBSERVATIONS ON THE SYNTHESIS OF ACETYLCHOLINE AND ON METABOLIC COMPARTMENTATION
Authors: Cheng S.‐C. 
Published: October 2006

Abstract— In the lobster nerve the fixation of CO, at various levels of pCO2 was studied by the incorporation of [l‐14C]pyruvate. Incorporation of 14C was solely dependent on CO2 fixation since the C‐1 was decarboxylated in the formation of acetyl‐CoA. Paired‐nerve studies with [2‐14C]pyruvate afforded a study of pyruvate metabolism in the lobster nerve. [I14C]Pyruvate was incorporated to nearly the same extent at all levels of pCO2 including zero pCO2, a finding that suggested metabolic recycling of CO2. The magnitude of the metabolic recycling of C‐1 of pyruvate or pyruvate dismutation was estimated to be nearly 20 per cent of total CO2 fixation. Re‐evaluation of the relative contributions of the CO2 fixation. and acetyl‐CoA pathways on the basis of more extensive data gave a ratio of 2:3.The pCO2 affected synthesis of ACh and the level of citrate. With increasing pCO2, the specific radioactivity of ACh decreased much more than the content of ACh. The decrease in the specific radioactivity of ACh but not that of citrate further suggested metabolic compartmentation. The implication of these findings is discussed.Alanine functioned as a metabolic sink for the incorporated pyruvate. Pyruvate levels were estimated to be approximately 0.1 nmol/mg of protein.
THE EFFECT OF TOPICAL APPLICATION OF DIETHYL‐α‐FLUOROGLUTARATE ON THE METABOLISM AND ELECTRICAL ACTIVITY IN VIVO OF CAT CEREBRAL CORTEX1
Authors: Cohen H. P. , Vasconetto C. , Ayala G.‐F. 
Published: October 2006

Abstract— The effect of topical application of diethyl‐α‐fluoroglutarate on the primary response of cat cerebral cortex to thalamic stimulation was investigated, and samples of the involved tissue and of homologous contralateral control tissue were removed at appropriate times for biochemical analyses. Changes in electrocortical response were first noted 30–40 min after topical application of 10 μ1 (52.7 μmol) of the drug to the pericruciate gyrus. A rapid reduction in amplitude of the surface negative component of the primary response was observed initially, followed by amplitude reduction and rapid disappearance of the primary response throughout the cortical field within a few minutes after the change first observed at the surface. The effects were interpreted either as a direct action of the drug on the somadendritic membrane or an inhibition of the excitatory synaptic impingement.Analyses of the tissues removed at the time of maximum electrocortical response indicated profound metabolic changes, including depletion of energy reserves and several Krebs cycle intermediates. Large increases in tissue levels of glucose, glucose 6‐phosphate, and pyruvate were found. Changes in amino acids comprised depletion of glutamate with increased tissue levels of aspartate, GABA, NH3, threonine, serine and alanine.Tissues were also removed at 10 min after topical application of the drug but before the advent of electrocortical changes. Decreased levels of glutamate were associated with a rise in tissue aspartate. Tissue levels of the other amino acids were unchanged. Glucose, glucose 6‐phosphate and pyruvate levels were increased, lactate and ATP levels were unchanged, and P‐creatine, α‐KG and malate levels were reduced. We believe that the observed pattern of changes represents responses of the cerebral cortex to either a block in the synthesis of glutamate or in oxidation of pyruvate, with consequent interference with oxidative and energy metabolism and eventual depression of cortical electrical activity.
THE EFFECTS OF ELECTRICAL STIMULATION AND IONIC ALTERATIONS ON THE METABOLISM OF AMINO ACIDS AND PROTEINS IN EXCISED SUPERIOR CERVICAL GANGLIA OF THE RAT1
Authors: McBride W. J. , Klingman J. D. 
Published: October 2006

Abstract— The effects of supramaximal electrical stimulation on the metabolism of amino acids and proteins in incubated superior cervical ganglia of the rat were studied by the use of a gas‐liquid chromatographic (GLC) assay procedure. Stimulation at 5 Hz for 2 h caused an apparent increase in tissue levels of free amino acids, with alanine, serine, glycine, valine, threonine, isoleucine and aspartate (+ asparagine) most noticeably affected. The amino acid composition (partial) of the TCA‐insoluble proteins of resting and stimulated ganglia was approximately the same after 60 min of incubation, but there was less TCA‐insoluble protein in the stimulated ganglia. The addition of amino acids (at plasma concentrations) to the standard media had no apparent affect on the amino acid composition of this protein fraction. Stimulation for 0, 5 h initially increased the efflux of alanine, valine, proline and ornithine into the incubation media but prolonged stimulation (for 4–0 h) decreased the efflux of alanine, serine, glycine and isoleucine and increased the efflux of lysine into the incubation media. The leakage of amino acids from the ganglia appeared to be a sodium‐dependent process.The incorporation of 14C from [U‐14C]glucose into glutamate (+ glutamine) and aspartate (+ asparagine) was greater in stimulated than in resting ganglia. However, the conversion of glutamate carbons from [U‐14C]l‐glutamate into aspartate was not affected by stimulation. Incorporation of 14C from [U‐14C]glucose into glycine and serine was apparently not affected by stimulation during the 60 min of incubation. However, serine was the only amino acid which exhibited a higher specific radioactivity in stimulated ganglia than in resting ganglia incubated for 4 h in standard media. Lithium ions had the apparent specific effect of increasing the labelling with 14C from [U‐14C]glucose into ornithine, and increasing the efflux and overall metabolism of serine in the ganglia. Incorporation of 14C from [U‐14C]glucose into proteins was lower in the stimulated than in the resting ganglia if compensation was made for the higher radioactivity available in the total free amino acid pool of the stimulated ganglia.The rate of 14C incorporation from [U‐14C]glutamate into the TCA‐insoluble proteins of resting ganglia was greater when no other amino acids at concentrations approximating plasma levels were added to the bathing media; this rate was lower in stimulated than in resting ganglia.
DIFFERENTIATION OF CHICK EMBRYO CEREBRAL HEMISPHERES: A CRITICAL EYALUATION OF A BULK PREPARATION OF NEUROBLASTS AND SPONGIOBLASTS
Authors: Judes C. , Jacob M. , Kister L. 
Published: October 2006

Abstract— A critical evaluation of a previously described method of bulk preparation of neuroblasts and spongioblasts from chick embryo cerebral hemispheres furnished the following results.

A major loss of total RNA occurs during the preparation of the cell fractions.
The loss occurred mainly during the dissociation of the tissue and the following centrifugations.
The missing RNA's were found in the supernatants after cell centrifugation at low speed.
There was a selective loss of transfer RNA amounting to 70–80 per cent relative to ribosomal RNA.
The relative proportions of the 29, 18 and 5s ribosomal RNA's were constant, but there was a decrease in their proportion relative to heavy‐molecular weight, rapidly‐labelled nuclear RNA.
The ribosomal RNA's in the low‐speed supernatant could be resedimented at 35,000 g whereas most transfer RNA could not.

The results are consistent with a loss of fragments of cytoplasm containing ribosomes and with additional extraction of transfer RNA during the preparation.
EFFECTS OF EXCITATION AND ANAESTHESIA ON THE GLUTAMINE CONTENT OF THE RAT BRAIN WITH A REFERENCE TO THE ADMINISTRATION OF GLUTAMINE
Authors: Dobkin J. 
Published: October 2006

Abstract— A study of the factors affecting the ghtamine content in brain of rats showed that it was significantly decreased by intraperitoneal injection of physiological saline and by the stimulus of decapitation. It fell markedly at the stage of delirium (excitement) of pentobarbitone sodium anaesthesia and returned to the original value in light and deep surgical anaesthesia; after pentylenetetrazol injection the glutamine content showed a tendency to decrease but this change was only significant in relation to its post‐saline level when the convulsant and 0.9 % NaCl were given to lightly‐anaesthetized animals.The i.p. administration of glutamine temporarily abolished the decrease in its concentration in the brain caused by injection and decapitation but never raised it above the original level. Many rats previously treated with glutamine showed no signs of excitement during the induction period of pentobarbitone sodium anaesthesia, and those which were excited showed a comparatively smaller decrease of brain glutamine content. whereas in the anaesthetic state there was no change in the content of brain glutamine after glutamine had been administered. Pentylenetetrazol given at the dose level of 200 mg/kg, but not at that of 100 mg/kg, resulted in the uptake of the added glutamine by the brain up to its normal concentration. Hence, the added glutamine did not readily enter normal or anaesthetized brain, but did penetrate the hyperactive brain where its level had fallen.The brain levels of free glutamic and aspartic acids were not affected, in general, by procedures which increased cerebral activity. Glutamate was decreased by deep anaesthesia, whereas aspartate was not significantly altered in any of the conditions which were tested.The significance of these results in relation to cerebral ammonia metabolism and possible changes of the permeability of the tissue to glutamine in different functional states is discussed.
BIOCHEMICAL EFFECTS OF THE ANTICONVULSANTS TRIMETHADIONE, ETHOSUXIMIDE AND CHLORDIAZEPOXIDE IN RAT BRAIN
Authors: Nahorski S. R. 
Published: October 2006

Abstract— The concentrations of several metabolites, including glucose, glycogen, hexose phosphates, adenine nucleotides phosphocreatine, amino acids and some tricarboxylate cycle intermediates, have been estimated in cerebral tissues of rats treated with anticonvulsant doses of trimethadione, ethosuximide and chlordiazepoxide.Anticonvulsant administration, in each case, produced an increase in brain glucose, but only trimethadione and ethosuximide resulted in elevated brain/blood glucose ratios. It was concluded that the apparent rise in intracellular glucose with the latter drugs may, in part, be the result of a stimulation of glucose transport from blood into the brain. Anticonvulsant administration was also shown to result in a depression of some tricarboxylate cycle intermediates. The pattern of these metabolite changes was in effect similar to those reported independently in mice treated with anaesthetics and it was therefore concluded that these differences probably reflected a depression in metabolic rate.Metabolic alterations in general do not indicate aetiology but rather effects of the drug activities. However, a role implicating increased intracellular glucose levels with membrane stabilization is discussed.
STUDIES ON THE INCORPORATION OF [14C]AMINO ACIDS INTO PROTEIN BY ISOLATED RAT BRAIN NUCLEI1
Authors: Dravid A. R. , Wong E. 
Published: October 2006

Abstract—Various parameters of the in vitro incorporation of [14C]amino acids into protein by cell nuclei isolated and purified from rat brain and liver were investigated. Nuclei purified through 2.2 m sucrose solution were capable of amino acid incorporation in vitro; and washing procedure to eliminate hypertonic sucrose before incubation was essential since sucrose in high concentration was inhibitory. Microbial contamination was found to be a serious source of error and the use of sterile conditions for incubation were necessary to obtain reproducible and valid results. Using completely sterile conditions, Na +, K+, RNase, DNase, puromycin, cycloheximide and chloramphenicol were without any effect on the ability of brain and liver nuclei to incorporate labelled amino acids into protein. Results of time‐course and preincubation experiments revealed that some factors essential for amino acid incorporation pass out of the nucleus into the medium. In addition, approximately 15 per cent of the labelled nuclear proteins with higher specific radioactivity was recovered in the incubation medium. Incorporation of [14C]leucine was proportional to the concentration of labelled amino acid and to the number of nuclei, and it is suggested that carefully controlled conditions of incubation are essential to obtain valid comparisons between different types of nuclei in terms of their relative abilities to incorporate amino acids in vitro. No evidence was obtained indicating isotope dilution phenomenon in these experiments. Whether or not in vitro incorporation of amino acid by nuclei represents protein synthesis is discussed.
THE ORIGIN OF THE ACETYLCHOLINE RELEASED FROM THE SURFACE OF THE CORTEX
Authors: Chakrin L. W. , Marchbanks R. M. , Mitchell J. F. , Whittaker V. P. 
Published: October 2006

Abstract—The specific radioactivity of acetylcholine liberated from the surface of the rabbit occipital cortex has been compared with that of the underlying cortical synaptosomal and vesicular acetylcholine at varying times after the administration of [N‐Me‐3H]choline. Choline was administered by diffusion from solutions placed in cups formed by Perspex cylinders applied to the surface of the cortex. Acetylcholine was collected by diffusion into these cups. The specific radioactivity of the acetylcholine declined progressively. The effect of stimulation of afferent cholinergic pathways was to cause a fall in the specific radioactivity of the released acetylcholine. However this was always higher than that of the synaptosomal or vesicular acetylcholine as represented by fractions P2 and D of the authors’fractionation scheme. It is concluded that acetylcholine released from the cortex must come from a store or stores more recently synthesized than the endogenous acetylcholine of these subcellular fractions.
MECHANISMS FOR THE EFFLUX OF [14C]DOPA AND [14C]DOPAMINE FROM THE CSF OF RHESUS MONKEYS
Authors: Shaywitz B. A. , Gormley W. T. , Arnold E. L. , Back K. C. 
Published: October 2006

Abstract—Clearance of [14C]DOPA and [14C]dopamine from CSF was investigated in anaesthetized rhesus monkeys (M. Mulatta) subjected to ventriculocisternal perfusion. The efflux coefficients, kVE, at tracer concentrations (3–5 m) in the perfusate were 0.0487 ml/min and 0.0325 ml/min for [14C]DOPA and [14C]dopamine, respectively. Carrier DOPA (10 mm) in the perfusate decreased the efflux of [14C]DOPAsignificantly, but carrier dopamine had no appreciable effect on the clearance of [14C]dopamine. These findings suggest that DOPA is cleared from CSF in part by a saturable mechanism which may be located in the choroid plexus, whereas dopamine leaves the ventricular system by passive diffusion. Radioactivity in the caudate nucleus immediately adjacent to the perfused ventricle averaged 15.5 % and 12.6% of the radioactivity in the perfusates with [14C]DOPA or [14C]dopamine, respectively. These distribution percentages were similar to those found for various extracellular indicators after ventriculocisternal perfusion and may indicate that the efflux of intraventricularly‐administered exogenous DOPA and dopamine occurs in part through extracellular channels.
THE REGIONAL DISTRIBUTION OF CYTIDINE 5′‐MONOPHOSPHO‐N‐ACETYL‐NEURAMINIC ACID SYNTHETASE IN CALF BRAIN
Authors: Van Den Eijnden D. H. , Meems L. , Roukema P. A. 
Published: October 2006

Abstract—The enzyme cytidine 5′‐monophospho‐N‐acetylneuraminic acid synthetase was studied in different parts of the calf brain. Characterization of partial purified enzyme preparations from cortical grey matter and corpus callosum by means of pH optima and Km values, showed the enzyme of grey and white brain areas to be identical. Unexpectedly the regional differences of the enzyme activities per g wet tissue and per mg protein were very slight. From the presence of the enzyme in pure white brain areas, which are known to be poor in neuronal perikarya, and the fact that the enzyme is localized in the cell nucleus, we concluded that cytidine 5′‐monophospho‐N‐acetylneuraminic acid is produced in glia cell nuclei and that it is very likely that biosynthesis of sialo‐glycoproteins and/or ganglio‐sides occurs within glia cells.The enzyme activity per μmol DNA‐P is somewhat higher in grey than in white regions, indicating a slightly higher activity per neuronal than per glial nucleus.The regional differences of lipid and protein‐bound sialic acid and RNA show a striking similarity and contrast to those of the enzyme. These differences are interpreted in terms of a differential content in neurons and glia cells.
SUBCELLULAR DISTRIBUTION OF PYRUVATE KINASE (EC 2.7.1.40) IN CEREBRAL CORTEX
Authors: Tamir H. , Kaufman H. , Rapport M. M. 
Published: October 2006

Abstract—The subcellular distribution of pyruvate kinase (EC 2.7.1.40) in the cerebral cortex of the rat was studied. The enzyme, which had been previously reported in the cytoplasm, was found to be present in synaptosomal, microsomal and mitochondrial fractions as well. The activity of the enzyme in the synaptosomal fraction was localized predominantly in the synaptosomal membrane and was not dissociated by repeated washing or recentri‐fuging in a sucrose gradient. Some kinetic parameters of the membrane‐associated pyruvate kinase were measured.
METABOLISM OF TRITIUM‐LABELLED PYRIDOXINE AND PYRIDOXINE 5′‐PHOSPHATE IN THE CENTRAL NERVOUS SYSTEM1
Authors: Tiselius H.‐G. 
Published: October 2006

Abstract— [3H]Pyridoxine and [3H]pyridoxine 5′‐phosphate have been injected into rats and mice. The uptake in brain tissue has been studied by comparing the concentrations of labelled compounds in serum, cerebrospinal fluid and brain tissue. Labelled pyridoxine passes rapidly into brain tissue, whereas the uptake of pyridoxine 5′‐phosphate occurs at a much slower rate.Perchloric acid extracts of brain have been fractionated by ion‐exchange chromatography and the distribution of isotope between the different forms of the vitamin has been determined at different times after the administration. The time sequence of the metabolic transformation is: pyridoxine+→ pyridoxine 5′‐phosphate → pyridoxal 5′‐phosphate → pyridoxamine 5′‐phosphate. After the initial transformation period about 40 per cent of the isotope is recovered in each of the pyridoxal 5′‐phosphate and pyridoxamine 5′‐phosphate fractions.
ACETYLCHOLINE SYNTHESIS FROM [2‐14C]PYRUVATE IN RAT STRIATAL SLICES
Authors: Lefresne P. , Guyenet P. , Glowinski J. 
Published: October 2006

Abstract— Rat striatal slices were incubated with [2‐14C]pyruvate or [6‐14C]glucose as sole carbon source. The method devised to study the accumulation of labelled ACh in tissues and incubating medium in the presence or absence of eserine 200 μM derived from the previous studies of FONNUM (1969) and Hemsworth and Morris (1964). Total ACh was estimated by biological assay.The specific activity of newly synthesized ACh was found to be equal to that of the precursors, even for short incubation times and low substrates concentrations. When slices were incubated with [2‐14C]pyruvate and eserine, the spontaneous release of ACh occurred at a constant rate, was not modified by the addition of 2 mM‐choline in the medium, and consisted only of newly synthesized transmitter.The initial rate of ACh synthesis was found to be independent of choline concentration, but dependent on the [2‐14C]pyruvate concentration, and reached a maximal value corresponding to about 5 per cent of the measured striatal choline acetyltransferase activity.The appearance of the so called ‘surplus ACh’ pool, obtained in the presence of eserine, could be detected only after 30 min and represented 26 per cent of the total tissue ACh content after 180 min of incubation.In the absence of eserine, tissue ACh levels increased six‐fold in 80 min and then remained stable until the end of the incubation period (180 min), if sufficient substrate was provided. The maximal ACh accumulation in slices was independent of both excess of choline and [2‐14C]pyruvate.The ‘ACh plateau’ represented the attainment of a new dynamic equilibrium, since ACh synthesis could still be stimulated by 30 mM‐K+. From these results, it was concluded that ACh synthesis is controlled by a negative feed‐back regulation.
MEMBRANE AFFINITIES AND SUBCELLULAR DISTRIBUTION OF THE DIFFERENT MOLECULAR FORMS OF CHOLINE ACETYLTRANSFERASE FROM RAT
Authors: Fonnum F. , Malthe‐Sørenssen D. 
Published: October 2006

AbstractCholine acetyltransferase from rat brain is present in three different molecular forms with isoelectric points at pH 7·4‐7.6, 7·7‐7·9 and 8·3. The three forms were identified in a highly purified enzyme preparation, in a preparation of synaptosomes and in a cyto‐plasmic preparation from disrupted axons and perikarya (fraction S3). The three molecular forms differed in their affinities for synaptosome membranes and for a cation exchange resin (CM‐Sephadex C‐50). The positive surface charges of the different molecular forms and their affinities for membranes correlated well with their isoelectric points. The molecular form with jsoelectric point 8·3 had the largest positive surface charge and the highest membrane affinity. On isoelectric focusing of an extract from rat brain synaptosomes, the molecular form with isoelectric point 8·3 formed a complex with a negatively charged compound, presumably a protein. A method was developed to remove this compound by treatment with DEAE‐Sephadex or by precipitation with vinblastine. These procedures are similar to methods known to remove the neurotubular protein. The complex formation did not occur in fraction S3.