bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE SYNTHESIS OF GLUTAMATE BY RAT BRAIN MITOCHONDRIA
Authors: Dennis S. G. C. , Clark J. B. 
Published: October 2006

Abstract—The synthesis of glutamate from 2‐oxoglutarate generated by the citric acid cycle and ammonium acetate has been studied in brain mitochondria of synaptic or non synaptic origin.Non synaptic brain mitochondria synthesise glutamate at twice the rate (1.3 nmol. min−1. mg protein−1) of synaptic mitochondria (0.65 nmol. min−1. mg protein−1) when pyruvate is the precursor for 2‐oxoglutarate, but at a similar rate (0.9 and 0.7 nmol. min−1, mg protein−1) when 3 hydroxybutyrate is the precursor.Glutamate synthesis from ammonium acetate and extramitochondrially addcd 2‐oxoglutarate (5 mM) by both synaptic and nonsynaptic mitochondria was 5‐fold higher (5‐6nmol. min−1. mg protein−1) than glutamate synthesis from endogenously produced 2‐oxoglutarate. In the uncoupled state (or un‐coupler + oligomycin) the rate was reduced by half. (2.5‐3 nmol. min−1. mg protein−1) as compared to mitochondria synthesising glutamate in states 3 or 4 (± oligomycin).The changes in brain mitochondrial nicotinamide nucleotide redox state have been monitored by fluorimetric, spectrophotometric and enzymatic techniques during glutamate synthesis and compared with liver mitochondria under similar conditions. On the instigation of glutamate synthesis by NH+4 addition a significant NAD(P)H oxidation occurs with liver mitochondria but no detectable change occurs with brain mitochondria.Leucine (2 mM) causes a doubling of glutamate synthesis by both synaptic and non synaptic brain mitochondria with no detectable change in the NAD(P)H redox state.The results are discussed with respect to the control of glutamate synthesis by mitochondrial redox potential and the possible intramitochondrial compartmentation of this process.
REGIONAL DISTRIBUTION OF HOMOCARNOSINE, HOMOCARNOSINE‐CARNOSINE SYNTHETASE AND HOMOCARNOSINASE IN HUMAN BRAIN
Authors: Kish Stephen J. , Perry Thomas L. , Hansen Shirley 
Published: October 2006

AbstractHomocarnosine (HCarn) content varied over a 6‐fold range in different regions of autopsied human brain, being highest in the dentate nucleus and the inferior olive, and lowest in the caudate nucleus and mesolimbic system. HCarn content was similar in biopsied and autopsied frontal cortex. Very little if any carnosine (Carn) was present in human brain, except for the olfactory bulb, where Carn may have comprised 20% of the imidazole dipeptides present. Only HCarn was present in human CSF.HCarn‐Carn synthetase enzyme activity in biopsy specimens of human frontal and temporal cortex was approx 10 times greater than has been reported for rat cerebral cortex. The enzyme synthesized Carn 3–5 times as rapidly as HCarn, when β‐alanine (β‐Ala) or GABA substrate concentrations were 10 MM. The synthetase was found to have an apparent Km of 1.8 mM for β‐Ala, and 8.8 mM for GABA. HCarn‐Carn synthetase activity decreases rapidly after brain death, and was not detectable in autopsied brain specimens frozen more than 6 h after patients’deaths.Homocarnosinase activity was determined in brain, using L‐[γaminobutyryl‐1‐14C]HCarn as substrate, and measuring radioactive GABA produced by hydrolysis of HCarn at pH 7.2 in the presence of Co2+ ions. Homocarnosinase activity was similar in biopsied and autopsied human cerebral cortex, and appeared to be stable for at least 10 h after death in unfrozen brain.Differences in the regional distribution of HCarn‐Carn synthetase and homocarnosinase activities, as well as regional differences in GABA content in human brain, do not readily account for regional differences in HCarn content, nor do they suggest a physiological role for HCarn.
REGIONAL DIFFERENCES IN LIPID COMPOSITION IN RABBIT NERVOUS TISSUE
Authors: Ishibe Takeshi , Yamamoto Akira 
Published: October 2006

AbstractLipid composition was determined for different regions of rabbit nervous tissue.In the white matter of adult rabbit, the ratio between cholesterol, phospholipids and sphingolipids was quite constant. Among the subclasses of phospholipids, phosphatidylcholine and sphingomyelin tended to compensate for each other as constituents of myelin, as did galactosphingolipids and sphingomyelin amongst the sphingolipids. The brain was rich in phosphatidylcholine and gakactosphingolipids, while peripheral nerves (PN) were rich in sphingomyelin. The spinal cord showed a composition intermediate between the brain and PN.The sphingolipid to phosphatidylcholine ratio seems to be useful as a myelin maturation index applicable to both CNS and PN.The rostral part of the CNS showed a high ratio of molecular species of cerebroside with α‐hydroxy fatty acids to those with unsubstituted fatty acids (CH/CN). The caudal part of the CNS had a high concentration of cerebrosides with C24‐monoenoic fatty acids, so that there was an inverse relationship between CH/CN and C24:1/C24:0 for different regions of CNS.The present data show that the lipid composition as well as the fatty acid composition of myelin‐specific lipids are influenced by neural differentiation and development or by neuroglial relationships.
SPIN LABEL STUDIES ON THE EFFECT OF ANESTHETICS IN SYNAPTIC MEMBRANES
Authors: Lenaz G. , Curatola G. , Mazzanti L. , Bertoli E. , Pastuszko A. 
Published: October 2006

AbstractWe have studied the effects of anesthetics on synaptic membranes obtained from pig brain by using stearic acid spin labels. The anesthetics used (butanol, halothane, ketamine) affect the rotational mobility of 16‐doxylstearate and the order parameter of 5‐doxylstearate. The changes in mobility of 16doxylstearate show a stronger fluidization in the membrane core than in vesicles of lipids extracted therefrom. This effect may be operationally described as a disruption of lipid‐protein interactions involving hydrophobic proteins. In fact no disordering is induced on the surface of synaptic membranes as shown by the order of Soioxylstearate, indicating a highly immobilized state of the lipids on the membrane surface. The results are discussed in view of our working hypothesis concerning the role of lipids in modulating protein conformation.
THE SUBUNIT STRUCTURE OF MAMMALIAN ACETYLCHOLINESTERASE: CATALYTIC SUBUNITS, DISSOCIATING EFFECT OF PROTEOLYSIS AND DISULPHIDE REDUCTION ON THE POLYMERIC FORMS
Authors: Vigny Marc , Bon Suzanne , Massoulié Jean , Gisiger Victor 
Published: October 2006

Abstract— An analysis of the [3H]DFP‐labelled catalytic subunits of mammalian (bovine SCG) acetylcholinesterase (AChE, EC 3.1.1.7.) indicates a monomer molecular weight of 75,000. This is equivalent to the mass previously determined for the smallest active form and demonstrates that the globular, or G forms, are respectively monomeric (G1 form, 4S), dimeric (G2 form, 6.5S) and tetrameric (G4 form, 10S). In the tetrameric G4 form the catalytic chains are associated in dimers, by disulphide bonds.The effect of reduction and proteolysis has shown that the dimeric form (G2 form, 6.5S) is readily reduced into G1, while the tetramer G4 is very stable, being only dissociated by a combination of reduction and proteolysis by high concentration of trypsin. The asymmetric forms A12 (16S), A8 (13S) and A4 (9S) are not sensitive to reduction, but are readily dissociated by low concentrations of trypsin, into each other, progressively liberating isolated tetramers. We obtained essentially identical results with AChE preparations from rat brain or superior cervical ganglion. These observations support a general model for the quaternary structure of acetylcholinesterase molecular forms.
UPTAKE OF MANGANESE BY CHROMAFFIN GRANULES IN VITRO
Authors: Daniels A. J. , Johnson L. N. , Williams R. J. P. 
Published: October 2006

Abstract– The distribution of metal ions in the chromaffin granule is anomalous. Calcium ions are accumulated but magnesium ions excluded. We have used the manganese ion as a convenient divalent element for following metal ion uptake because it can usefully be employed as a substitute for magnesium.The kinetics of the manganese incorporation were followed by radio tracer technique and its transport was characterized as being non‐energy dependent and having a small thermal activation factor. The presence in the incubation medium of a membrane‐bound ATPase inhibitor (NEM) or addition of CN− or NaN3 did not affect the metal incorporation into chromaffin granules. Little endogenous magnesium exchanges for manganese when the latter is incorporated, but magnesium competitively prevented manganese uptake. The binding of manganese inside the vesicle was strong and it was not exchangeable with magnesium even in the presence of ATP.Manganese when incorporated binds to ATP and displaces catecholamines resulting in a decrease in the CA/ATP ratio.
THE PURIFICATION AND PROPERTIES OF RAT BRAIN GLUTAMATE DEHYDROGENASE
Authors: Chee Po Yok , Dahl June L. , Fahien Leonard A. 
Published: October 2006

Abstract—A method is described for the preparation of glutamate dehydrogenase in a highly purified form from rat brain. Only one protein band was detected when the enzyme was subjected to electrophoresis on SDS polyacrylamide gels. The rat brain enzyme was essentially identical to the rat liver enzyme with respect to electrophoresis on SDS polyacrylamide gels, immunochemical properties and most kinetic parameters. However, the brain enzyme was much less reactive with glutamate, was more sensitive to inhibition by haloperidol, and was considerably more stable than the liver enzyme.
Accumulations of Cyclic AMP in Adenine‐Labeled Cell‐free Preparations from Guinea Pig Cerebral Cortex: Role of α‐Adrenergic and H1‐Histaminergic Receptors
Authors: Daly J. W. , McNeal E. , Partington C. , Neuwirth M. , Creveling C. R. 
Published: October 2006

AbstractNorepinephrine, histamine, adenosine, glutamate, and depolarizing agents elicit accumulations of radioactive cyclic AMP from adenine‐labeled nucleotides in particulate fractions from Krebs‐Ringer homogenates of guinea pig cerebral cortex. The particulate fractions contain sac‐like entities, which apparently are associated with a significant portion of the tnembranal adenylate cyclase. Particulate fractions from sucrose homogenates are a less effective source of such responsive entities. Activation of the adenine‐labeled cyclic AMP‐generating systems by norepinephrine is by means of α‐adrenergic receptors, while activation by histamine is through H1‐ and H2‐histaminergic receptors. Adenosine responses are potentiated by the amines and are antagonized by alkylxanthines. Glutamate and depolarizing agents appear to elicit accumulations of cyclic AMP via „release” of endogenous adenosine. It is proposed, based on the virtual absence of an α‐adrenergic or H1‐histaminergic response in the presence of a combination of potent adenosine and H2‐histaminergic antagonists, that α‐adrenergic and H1‐histaminergic receptor mechanisms do not activate adenylate cyclase directly in brain slices or Krebs‐Ringer particulate fractions, but merely facilitate activation by β‐adrenergic, H2‐histaminergic, or adenosine receptors.
Measurement of Free Glucose Turnover in Brain
Authors: Savaki H. E. , Davidsen L. , Smith C. , Sokoloff L. 
Published: October 2006

AbstractA method has been developed for the measurement of the turnover rate constant or the half‐life of the free glucose content of brain. It is based on an equation derived by the mathematical analysis of a kinetic model of the equilibration of the specific activity of the free glucose in brain with that of the plasma during an infusion of radioactive glucose. The method requires the measurement of the time course of the specific activity of glucose in the arterial plasma during an intravenous infusion of radioactive glucose for a period of 1 to 4 min and the specific activity of the free glucose in brain at the termination of the infusion. The turnover rate constant, or the half‐life, is then calculated from these data by means of the operational equation of the method. The technique has been applied to conscious and anesthetized rats. In conscious rats the half‐life of the free glucose content of brain was found to be 1.6 ± 0.5 min (mean ±s.d.) when the animals were killed by decapitation and 1.2 ± 0.2 min (mean ±s.d.) when they were killed by microwave irradiation; this difference is not statistically significant. In anesthetized rats, the half‐life was found to be 2.6 ± 0.8 min (mean ±s.d.) in those killed by decapitation and 1.8 ± 0.3 min (mean ±s.d.) in those killed by microwave irradiation; this difference is statistically significant. The half‐life of the glucose content of brain was found to be significantly prolonged during anesthesia and to be significantly and positively correlated with the plasma glucose concentration (r= 0.78; p < 0.001).
Immunochemical Characterization of Bovine Brain Cathepsin D
Authors: Whitaker John N. 
Published: October 2006

Abstract:Antibodies to bovine brain cathepsin D were produced in rabbits and guinea pigs and utilized to characterize this enzyme immunochemically. By immunodiffusion, broad organ–but limited species–cross‐reactivity was demonstrated with antisera to the brain enzyme. On immunoelectrophoresis the immunoreactive material migrated as a single are in the beta‐gamma region. In a double antibody radioimmunoassay, which had a sensitivity for cathepsin D of 1 ng of immunoreactive enzyme per assay tube, no inhibition was produced by pepstatin, bovine myelin basic protein, or bovine basic protein peptides 1‐42, 43‐88 or 89‐169. Comparative studies of enzymatic and immunoreactive activity of bovine brain cathepsin D demonstrated a close correlation, but the immunoassay was much more sensitive in detecting the presence of enzyme protein. Immunoreactivity persisted unaltered under conditions that abolished or reduced enzymatic activity. Antibodies to brain cathepsin D inhibited the activity of the enzyme on a hemoglobin substrate at pH 5. On gel filtration of bovine brain homogenate, the immunoreactivity, measured by either radial immunodiffusion or radioimmunoassay, and enzymatic activity of cathepsin D coeluted, indicating a molecular weight of approximately 42,000. However, immunofixation of enzyme on polyacrylamide slab gels subjected to electrophoresis in the presence of sodium dodecyl sulfate demonstrated bands of immunoreactivity in purified enzyme in the molecular weight ranges of 42,000, 31,000 and 13,000 and two very faint bands in the range of 32,000‐36,000. Immunofixation also revealed antigen in 42,000 and 31,000 molecular weight species of homogenates of bovine brain, liver, spleen, and kidney.
Transport of Catecholamines by Native and Reconstituted Rat Heart Synaptic Vesicles
Authors: Angelides Kimon J. 
Published: October 2006

Abstract:Highly purified “heavy” synaptic vesicles were isolated from rat heart by differential centrifugation. Because of the high intravesicular concentrations of proteins, catecholamine, and ATP, resealed vesicle ghosts were prepared and used to study the detailed kinetics of catecholamine transport. ATP stimulated the uptake of /‐norepinephrine and was saturable with a Km for l‐norepinephrine at 3.3 μM and 1.8 mM for ATP. The ghosts also accumulated 5‐hydroxytryptamine and l‐epinephrine via an ATP‐dependent mechanism. Uptake was stereospecific for the l‐form. A functional catecholamine transporter could be solubilized by the detergent octyl‐glucoside and incorporated into phospholipid vesicles, which, after detergent removal, generated proteoliposomes that accumulated l‐norepinephrine. Reserpine‐ and l‐propranolol‐sensitive accumulation against a concentration gradient is achieved by artificially creating a pH gradient across the membrane, and lends further support to the idea that at least the initial phase of catecholamine transport is driven by the trans‐membrane pH gradient created by the proton‐translocating ATPase.
Modulation of the Distribution of Acetylcholinesterase Molecular Forms in a Murine Neuroblastoma × Sympathetic Ganglion Cell Hybrid Cell Line
Authors: Lazar Monique , Vignyt Marc 
Published: October 2006

Abstract:Studies were carried out on the polymorphism of acetylcholinesterase (AChE, EC 3.1.1.7) in a neuroblastoma × sympathetic ganglion cell hybrid cell line (T28) and its parental clone (N18TG2). These cells contain the tetrameric (G4, 10S), dimeric (G2, 6.5S), and monomeric (GI, 4S) forms of AChE, but not the collagen‐tailed A12 (16S) form of the sympathetic ganglion. Three variants of these forms could be distinguished on the basis of their solubility properties: (i) secreted forms which do not interact with the detergent Triton X‐100; (ii) cellular forms which may be solubilized in detergent‐free buffer and which interact reversibly with Triton X‐100; (iii) cellular forms which require detergent for solubility, and aggregate in its absence. By using a nonpenetrating inhibitor, we demonstrated that, in T28 stationary cells, the cellular G4 form is associated with the plasma membrane, whereas the G1 form is intracellular. During induction of AChE activity in T28 cells, the relative proportion of the G4 form increases, suggesting, in agreement with previous observations, that GI is a metabolic precursor of G4. The evolution of AChE molecular forms released into the culture medium closely resembles that of the cellular forms. The preferential accumulation of the G4 molecules does not simply depend on the cellular level of G1. It is favoured by culture conditions which promote morphological differentiation, but does not require the actual extension of neurites. T28 cells as well as other neuroblastoma‐derived cells appear to be useful experimental materials to investigate the regulatory mechanisms underlying the maturation of AChE globular forms.
Amino Acid Changes in a Genetic Strain of Epileptic Beagle Dogs
Authors: van Gelder N. M. , Edmonds H. L. , Hegreberg G. A. , Chatburn C. C. , Clemmons R. M. , Sylvester D. M. 
Published: October 2006

Abstract:A neurochemical evaluation of beagle dogs with naturally occurring spontaneous generalized convulsive seizures was performed. Amino acid profiles of serum, cerebrospinal fluid (CSF), and biopsied cerebral cortex from epileptic dogs were compared with those from seizure‐free siblings. No differences in absolute levels were noted. However, when levels were normalized as a percent of total free amino acids, the two groups differed in certain respects. Ten significant correlations between amino acid pairs appeared in epileptic dogs, but only one was seen in seizure‐free animals. Seven of these ten corretions involved glutamate or taurine. It was noted that the highly correlated amino acids (taurine, glutamate, glycine, glutamine, alanine) all utilize sodium‐dependent membrane transport processes. The sum of glutamate, aspartate, and glycine levels (competing sodium‐dependent high‐affinity systems) was significantly lower in epileptic beagles. Since this difference was noted in serum but not CSF or brain, it may indicate a diminished capacity of sodium‐dependent high‐affinity renal transport for acidic and certain small neutral amino acids.
Presynaptic Control of the Synthesis and Release of Dopamine from Striatal Synaptosomes: A Comparison Between the Effects of 5‐Hydroxytryptamine, Acetylcholine, and Glutamate
Authors: de Belleroche J. S. , Bradford H. F. 
Published: October 2006

Abstract:The effects of 5‐HT and glutamate on dopamine synthesis and release by striatal synaptosomes were investigated and compared with the action of acetylcholine, which acts presynaptically on this system. 5‐HT inhibited (28%) synthesis of [14C]dopamine from L‐[U‐14C]tyrosine, at 10‐5M and above. This contrasts with the action of acetylcholine, which stimulated [14C]‐dopamine synthesis by 24% at 10‐4 M. Tissue levels of GABA were unaffected by either 5‐HT or acetylcholine up to concentrations of 10‐4 M. The inhibitory action of 5‐HT (5 × 10−5 M and 2 × 10−4 M) on [19C]dopamine synthesis was completely abolished by methysergide (2 × 10−6 M). Higher concentrations of methysergide (10−4 M) or cyproheptadine (10−5 M) inhibited [14C]dopamine synthesis by 28% and 25%, respectively, when added alone to synaptosomes. However, only methysergide prevented the further inhibition of synthesis caused by 5‐HT.At concentrations of 2 × 10−5 M and above, 5‐HT stimulated [14C]dopamine release. This releasing action differed from that of acetylcholine, which occurred at lower concentrations (e.g., 10−6 M). Methysergide (up to 10−4 M) or cyproheptadine (2 × 10−4 M) did not reduce the 5‐HT (5 × 10−5 M)‐induced release of [14C]dopamine, but methysergide (10−4 M) showed a potentiation (49%) of this increased release. The stimulatory effects of 5‐HT (2 × 10−5 M) and K+ (56 mM) on [14C]dopamine release were additive, indicating that two separate mechanisms were involved. However, when both agents were present the stimulatory effect of K+ (56 mM) on [14C]dopamine synthesis was not seen above the inhibitory effect of 5‐HT. Glutamate (0.1‐5 mM) did not affect [4C]dopamine release or its synthesis from L‐[U‐14C]tyrosine.It is concluded that 5‐HT modulates the synthesis of dopamine in striatal nerve terminals through a presynaptic receptor mechanism, an action antagonised by methysergide. The releasing action of 5‐HT apparently occurs through a separate mechanism which is also distinct from that involved in the response to K+ depolarisation.
Effects of a Single Therapeutic Dose of Glycerol on Cerebral Metabolism in the Brains of Young Mice: Possible Increase in Brain Glucose Transport and Glucose Utilization
Authors: Thurston Jean Holowach , Hauhart Richard E. , Dirgo John A. 
Published: October 2006

Abstract: This is a study of the effects of a single “therapeutic” dose of glycerol [2 g(22 mmol)/kg i.p.] on brain carbohydrate and energy metabolism in normal nursing weanling mice. Findings were correlated with brain water and electrolyte content and with metabolite changes in plasma, red blood cells, and liver.Plasma glycerol levels peaked at 21 mM 7.5 min after injection and returned to the control value, 0.16 mM, by 2 h. Plasma Na+ concentration decreased and plasma protein increased for as long as 2 h after injection. Although red blood cells were freely permeable to glycerol, there was no evidence for glycerol metabolism in these cells. Glycerol levels in liver paralleled those in plasma. Glycerol injection increased liver glucose concentration 23% and doubled hepatic glycerol‐1‐phosphate levels. Liver ATP levels were reduced 24% after glycerol injection.Brain water concentration was significantly reduced from 7.5 min to 30 min after glycerol injection; brain Na+ and K+ levels were unchanged. There was no evidence for glycerol entry into brain (the amount detected in brain tissue could be explained by the glycerol content in the blood of the brain). While plasma glucose increased 33%, brain glucose increased 87%. Concomitantly there were statistically significant increases in fructose‐1,6‐diphosphate, lactate, α‐ketoglutarate, and malate levels.The disproportionately high brain glucose value suggests increased transport of glucose from the blood to the brain. Increases in fructose‐1,6‐diphosphate, lactate, α‐ketoglutarate, and malate are compatible with an increased metabolic flux in the glycolytic pathway and Krebs citric acid cycle. As has been previously shown for urea and/or mannitol, these changes may result from the effects of the hyperosmolar glycerol solution on the blood‐brain barrier and on cerebral glucose utilization.The sustained lowering of plasma Na+ concentration after a single “therapeutic” glycerol injection suggests a need for monitoring plasma Na+ levels in the clinical situation. Possible lowering of hepatic ATP levels by the use of glycerol in humans is another concern.