Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The principles of immunocytochemistry were outlined in 1942 by Coons et al. and in the 1970's immunocytochemistry emerged as a powerful method for identifying structures and tracing pathways in the nervous system. It now plays a fundamental role in the neuroanatomical and histochemical analysis of the central nervous system. The first immunocytochemical studies of the mammalian cochlea were reported in 1980, from three different laboratories. Since then many studies on cochlear immunocytochemistry have been carried out, concerned with questions about neurotransmitter candidates or about structural proteins. This review describes immunoreactivity of enkephalin, choline acetyltransferase (ChAT), glutamate decarboxylase (GAD), gamma-aminobutyric acid (GABA), aspartate aminotransferase (AATase) and glutaminase (GLNase) in the organ of Corti. ChAT is the enzyme that catalyzes the synthesis of acetylcholine (ACh). GAD is the terminal enzyme in the biosynthesis of the inhibitory neurotransmitter GABA. AATase and GLNase are two enzymes involved in the metabolism of the excitatory neurotransmitter candidates aspartate and glutamate. We have much relied on surface preparations of the organ of Corti. We have also used cryostat sectioning of the cochlea, particularly when there was a need to apply a number of different antisera to comparable preparations from one and the same cochlea. We have used immunofluorescence and immunoperoxidase procedures. Immunoperoxidase procedures have given us better signal noise ratio for specific immunoreactivity (in surface preparations) than has immunofluorescence. Occasionally, to achieve maximal resolution of surface preparations in light microscopy studies, we have used enhanced contrast video display. We have found immunoreactivity in efferent fibers in the organ of Corti following the application of antisera to enkephalin, ChAT, GAD, GABA, AATase and GLNase. Most of these different antisera give different distributions of immunoreactivity and other antisera have evoked no immunoreactivity in the organ of Corti. To the best of our knowledge, the cells of origin of efferent axons and terminals in the organ of Corti are located in the brainstem. Originally described as crossed and uncrossed olivocochlear neurons, these efferents have recently been classified into a medial and a lateral system predominantly innervating, respectively, the outer hair cell region and the inner hair cell region. However, our findings on the distribution of GAD- and GABA-like immunoreactivity indicate that there may be more than two different systems of efferents in the organ of Corti, as previously suggested by Schwartz and Ryan (1983).
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PMID:Neurotransmitter-related immunocytochemistry of the organ of Corti. 287 25

Glutamate and aspartate are putative excitatory neurotransmitters in the central nervous system. The present study utilized novel monoclonal antibodies against fixative-modified glutamate and aspartate and polyclonal antisera against the amino acid synthesizing enzymes, glutaminase and aspartate aminotransferase, to analyze the distribution of these amino acids in the rodent midbrain periaqueductal gray. Glutamate-, aspartate-, glutaminase- and aspartate aminotransferase-like immunoreactive neurons, fibers and processes are present throughout the rostrocaudal length of the periaqueductal gray. Glutamate- and glutaminase-like immunoreactive neurons displayed a similar homogeneous pattern of distribution, being localized predominantly to the lateral and dorsal subdivisions of the periaqueductal gray. Co-localization experiments suggest that glutamate and glutaminase are in fact co-contained within the same PAG neurons. Aspartate aminotransferase-like immunoreactive neurons were distributed in a pattern similar to glutamate and glutaminase with the exception that fewer cells were stained in the dorsocaudal and the rostral third of the PAG. Aspartate-like immunoreactive neurons were less numerous than glutamate-like immunoreactive cells and were located in the lateral aspect of the PAG. These results demonstrate a specific and distinct distribution of glutamate and aspartate immunoreactive neurons and support recent data suggesting that glutamate and aspartate serve as excitatory neurotransmitters in the PAG.
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PMID:Localization of glutamate, glutaminase, aspartate and aspartate aminotransferase in the rat midbrain periaqueductal gray. 288 81

The intra-cochlear distributions of aspartate aminotransferase and glutaminase, prominent enzymes of aspartate and glutamate metabolism, have been studied by quantitative microchemical techniques. Also measured was choline acetyltransferase, the enzyme synthesizing acetylcholine, and a marker for the olivocochlear bundle. Aspartate aminotransferase activity was highest in the stria vascularis, about half this high in the organ of Corti synaptic (hair cell) zones, somewhat lower in the organ of Corti non-synaptic (Hensen's cell) zones, lower yet in Reissner's and lowest in the tectorial membrane. Glutaminase, on the other hand, had its highest activity in synaptic zones, about a third of that activity in the organ of Corti non-synaptic zones, and a barely detectable activity in Reissner's and tectorial membranes, and stria vascularis. Seven days after transection of the olivocochlear bundle, no significant difference was found between lesion- and control-side aspartate aminotransferase or glutaminase activities, even though no choline acetyltransferase activity remained in the lesion-side of the organ of Corti. Both the distribution of aspartate aminotransferase activity and the lesion results would seem to implicate it in energy more so than neurotransmitter metabolism. The distribution of glutaminase activity could be consistent with a role in neurotransmission; however, the lesion data were unable to demonstrate a specific association with the olivocochlear bundle.
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PMID:Quantitative distributions of aspartate aminotransferase and glutaminase activities in the rat cochlea. 302

The mechanism by which pentylenetetrazole provokes convulsions in animals has been investigated by measuring its influence in vitro on the activities of several enzymes of glutamate metabolism in rat brain homogenates. Pentylenetetrazole does not affect the specific activities of glutamine synthetase, glutaminase, or glutamate decarboxylase; it inhibits those of glutamate dehydrogenase and aspartate aminotransferase, and stimulates that of gamma-aminobutyric acid (GABA) aminotransferase. The overall consequence of the action of pentylenetetrazole on the activities of these enzymes should be an increase in the concentration of glutamate and a decrease in that of GABA. This modulation of glutamate and GABA metabolism by pentylenetetrazole could contribute to the triggering of convulsions.
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PMID:Pentylenetetrazole inhibits glutamate dehydrogenase and aspartate aminotransferase, and stimulates GABA aminotransferase in homogenates from rat cerebral cortex. 321 59

The distributions of glutaminase and aspartate aminotransferase were studied immunocytochemically in the cerebellum of the guinea pig and the rat. In the granule cell layer, both antibodies gave a similar staining pattern. Granule cell bodies were labeled, but staining was also found to lie outside the cell body, associated with what appear to be synaptic processes. In the molecular and Purkinje cell layers, aspartate aminotransferase was concentrated in stellate and basket cell bodies and in terminal baskets beneath Purkinje cells. Glutaminase, however, was not concentrated in these structures.
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PMID:Immunocytochemical localization of aspartate aminotransferase and glutaminase immunoreactivities in the cerebellum. 351 Jun 91

1. Glutamate dehydrogenase, aspartate transaminase and alanine transaminase were present in the gill, liver and muscle tissues of Periophthalmodon schlosseri and Boleophthalmus boddaerti. Both transaminases were found in the cytosol and mitochondria. 2. A complete purine nucleotide cycle was not present in the tissues studied. 3. Glutamine synthetase was not detected. Phosphate-dependent glutaminase was detected in both the cytosol and mitochondria. 4. Aspartate was the major substrate of ammoniagenesis in the mudskippers, though glutamate and glutamine were also oxidised. 5. Transdeamination was the major pathway for ammoniagenesis in the mudskippers studied.
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PMID:Ammoniagenesis in mudskippers Boleophthalmus boddaerti and Periophthalmodon schlosseri. 366 40

In lymphocytes of the rat, pyruvate kinase, phosphoenolpyruvate carboxykinase and NADP+-linked malate dehydrogenase (decarboxylating) are distributed almost exclusively in the cytosol whereas pyruvate carboxylase is distributed almost entirely in the mitochondria. For NAD+-linked malate dehydrogenase and aspartate aminotransferase approximately 80% and 40%, respectively, are in the cytosolic compartment. Since glutaminase is present in the mitochondria, glutamine is converted to malate within the mitochondria but further metabolism of the malate is likely to occur in the cytosol. Hence pyruvate produced from this malate, via oxaloacetate and phosphoenolpyruvate carboxykinase, may be rapidly converted to lactate, so restricting the entry of pyruvate into the mitochondria and explaining why very little glutamine is completely oxidised in these cells despite a high capacity of the Krebs cycle.
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PMID:Intracellular distribution of some enzymes of the glutamine utilisation pathway in rat lymphocytes. 374 15

There is considerable evidence that pathways of the hippocampus use an excitatory amino acid as transmitter. We have attempted to immunocytochemically identify excitatory amino acid neurons in the hippocampus of the rat and guinea pig using antiserum to glutaminase and antiserum to aspartate aminotransferase, which have been proposed as markers for aspartergic/glutamergic neurons. Glutaminase-like immunoreactivity was seen in granule cells in the dentate gyrus and fibers and puncta associated with the mossy fiber pathway in the hilus and stratum lucidum of the hippocampus. At the ultrastructural level, glutaminase-like immunoreactivity was observed in mossy fiber terminals in the stratum lucidum. Glutaminase-like immunoreactivity was also seen in pyramidal cells in regio inferior and regio superior and in cells in layer two of the entorhinal cortex. Schaffer collateral terminals, commissural fiber terminals and perforant pathway terminals were not seen at the light microscopic level. Glutaminase-like immunoreactivity is thus found in the cell bodies of proposed excitatory amino acid neurons of hippocampal pathways, but does not appear to label all terminals. Aspartate aminotransferase-like immunoreactivity was not seen in any cells, fibers or terminals in the rat or guinea pig hippocampus.
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PMID:Immunocytochemical localization of glutaminase-like and aspartate aminotransferase-like immunoreactivities in the rat and guinea pig hippocampus. 388 76

Glutamate has long been considered to be a neurotransmitter candidate in vertebrate spinal sensory nerve cells. We report here the first immunohistochemical evidence in support of this hypothesis. We find that up to 30% of the moderately small dorsal root ganglion neurons in the rat contain elevated levels of glutaminase immunoreactivity. This enzyme, which mediates the synthesis of glutamate from glutamine, is not found at these high levels in large diameter neurons of the same ganglia. In contrast, another enzyme associated with glutamate metabolism, aspartate aminotransferase, is rather uniformly distributed within neurons of the sensory ganglia. These data define a subpopulation of sensory neurons which appear to contain an elevated capacity to synthesize glutamate through the glutamine cycle and suggest that glutaminase immunoreactivity may be an indicator of glutamatergic function in some nerve cells.
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PMID:Localization of elevated glutaminase immunoreactivity in small DRG neurons. 389 Oct 15

Glutamine is utilized at a high rate (fourfold higher than that of glucose) by isolated incubated lymphocytes and produces glutamate, aspartate, lactate and ammonia. The pathway for glutamine metabolism includes the reactions catalysed by glutaminase, aspartate aminotransferase, oxoglutarate dehydrogenase, succinate dehydrogenase, fumarase, malate dehydrogenase and phosphoenolpyruvate carboxykinase. In fact little if any of the carbon of the glutamine that is used is converted to acetyl-CoA for complete oxidation. For this reason, the oxidation of glutamine is only partial and, in an analogous manner to the terminology used to describe the partial oxidation of glucose to lactate as glycolysis, the term glutaminolysis is used to describe the process of partial glutamine oxidation. The role of glutaminolysis in lymphocytes and perhaps other rapidly dividing cells is to provide both nitrogen and carbon for precursors for synthesis of macromolecules (e.g. purines and pyrimidines for DNA and RNA) and also energy. However, the rate of glutamine utilization by lymphocytes is markedly in excess of the precursor requirements (which are at most 4%) and if glutamine was vitally important in energy production it would be expected that more would be converted to acetyl-CoA for complete oxidation via the Krebs cycle. Indeed most of the energy for lymphocytes may be obtained by the complete oxidation of fatty acids and ketone bodies. Consequently the role of the high rate of glutaminolysis in lymphocytes and other rapidly dividing cells may be identical to that of glycolysis: the high rates provide ideal conditions for the precise and sensitive control of the rate of use of the intermediates of these pathways for biosynthesis when required. High rates of glycolysis and glutaminolysis can be seen as part of a mechanism of control to permit synthesis of macromolecules when required without any need for extracellular signals to make more glucose or glutamine available for these cells. In order to maintain a high rate of glutaminolysis despite fluctuation in the plasma level of glutamine, the flux through the glutaminolytic pathway can be controlled and the key processes in the lymphocyte that may play a role in this process include glutamine transport across the cell and mitochondrial membranes, glutaminase and oxoglutarate dehydrogenase. Changes in the intracellular concentration of Ca2+ may play a role in control of one or more of these reactions.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Glutamine metabolism in lymphocytes: its biochemical, physiological and clinical importance. 390 97


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