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Nielsen TT, Støttrup NB, Løfgren B, Bøtker HE. Metabolic fingerprint of ischaemic cardioprotection: importance of the malate-aspartate shuttle. Cardiovasc Res 2011; 91:382-91. [PMID: 21349875 DOI: 10.1093/cvr/cvr051] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The convergence of cardioprotective intracellular signalling pathways to modulate mitochondrial function as an end-target of cytoprotective stimuli is well described. However, our understanding of whether the complementary changes in mitochondrial energy metabolism are secondary responses or inherent mechanisms of ischaemic cardioprotection remains incomplete. In the heart, the malate-aspartate shuttle (MAS) constitutes the primary metabolic pathway for transfer of reducing equivalents from the cytosol into the mitochondria for oxidation. The flux of MAS is tightly linked to the flux of the tricarboxylic acid cycle and the electron transport chain, partly by the amino acid l-glutamate. In addition, emerging evidence suggests the MAS is an important regulator of cytosolic and mitochondrial calcium homeostasis. In the isolated rat heart, inhibition of MAS during ischaemia and early reperfusion by the aminotransferase inhibitor aminooxyacetate induces infarct limitation, improves haemodynamic responses, and modulates glucose metabolism, analogous to effects observed in classical ischaemic preconditioning. On the basis of these findings, the mechanisms through which MAS preserves mitochondrial function and cell survival are reviewed. We conclude that the available evidence is supportive of a down-regulation of mitochondrial respiration during lethal ischaemia with a gradual 'wake-up' during reperfusion as a pivotal feature of ischaemic cardioprotection. Finally, comments on modulating myocardial energy metabolism by the cardioprotective amino acids glutamate and glutamine are given.
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Affiliation(s)
- Torsten Toftegaard Nielsen
- Department of Cardiology, Skejby Hospital, Aarhus University Hospital, Brendstrupgaardsvej 100, Aarhus N, Denmark.
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McKenna MC, Waagepetersen HS, Schousboe A, Sonnewald U. Neuronal and astrocytic shuttle mechanisms for cytosolic-mitochondrial transfer of reducing equivalents: current evidence and pharmacological tools. Biochem Pharmacol 2005; 71:399-407. [PMID: 16368075 DOI: 10.1016/j.bcp.2005.10.011] [Citation(s) in RCA: 232] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Revised: 09/30/2005] [Accepted: 10/04/2005] [Indexed: 11/17/2022]
Abstract
The malate-aspartate shuttle and the glycerol phosphate shuttle act to transfer reducing equivalents from NADH in the cytosol to the mitochondria since the inner mitochondrial membrane is impermeable to NADH and NAD+. This transfer of reducing equivalents is essential for maintaining a favorable NAD+/NADH ratio required for the oxidative metabolism of glucose and synthesis of neurotransmitters in brain. There is evidence that both the malate-aspartate shuttle and glycerol phosphate shuttle function in brain; however, there is controversy about the relative importance and cellular localization of these shuttles. The malate-aspartate shuttle is considered the most important shuttle in brain. It is particularly important in neurons and may be extremely low, or even non-existent in brain astrocytes. Several studies provide evidence of glycerol phosphate shuttle activity in brain cells; however, the activity of this shuttle in brain has been questioned. A number of pharmacological tools, including aminooxyacetic acid, beta-methyleneaspartate, phenylsuccinate, and 3-nitropropionic acid, have been used to inhibit the four enzymes and two carrier proteins that participate in the malate-aspartate shuttle. Although no drugs completely inhibit the glycerol phosphate shuttle, evidence for the existence of this shuttle is provided by studies using drugs to inhibit the malate-aspartate shuttle. This report evaluates the evidence for each shuttle in brain cells and the drugs that can be used as pharmacological tools to study these shuttles.
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Affiliation(s)
- Mary C McKenna
- Department of Pediatrics, University of Maryland School of Medicine, 655 West Baltimore Street, Room 10-031, Baltimore, MD 21201-1509, USA
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3
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Dunlop J, Grieve A, Damgaard I, Schousboe A, Griffiths R. Sulphur-containing excitatory amino acid-evoked Ca2+-independent release of d-[3H]aspartate from cultured cerebellar granule cells: The role of glutamate receptor activation coupled to reversal of the acidic amino acid plasma membrane carrier. Neuroscience 1992; 50:107-15. [PMID: 1357589 DOI: 10.1016/0306-4522(92)90385-f] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Sulphur-containing excitatory amino acid transmitter candidates (500 microM) stimulated the Ca(2+)-independent efflux of exogenously-supplied D-[3H]aspartate from primary cultures of cerebellar granule cells superfused continuously with HEPES-buffered saline containing CoCl2 (1 mM) in place of CaCl2. The stimulated release of D-[3H]aspartate was markedly attenuated by 200 microM 6,7-dinitroquinoxalinedione, a concentration at which the antagonist inhibits both non-N-methyl-D-aspartate and N-methyl-D-aspartate ionotropic excitatory amino acid receptors. The Ca(2+)-independent component of evoked release was also markedly attenuated and, in some cases, abolished by removing NaCl from the superfusion medium. Furthermore, when 700 microM dihydrokainate (demonstrated herein as a mixed/non-competitive inhibitor of the high-affinity dicarboxylic amino acid transporter in cultured granule cells) was included in the superfusion medium, stimulated efflux of D-[3H]aspartate was reduced by between 15-78% of the control response; the extent of inhibition varying with the agonist employed. In constrast, agents which act as competitive inhibitors of the plasma membrane carrier in granule cells, e.g. beta-methylene-D,L-aspartate, potentiated the release of D-[3H]aspartate in a synergistic manner. Taken together, these findings are consistent with a mechanism for the Ca(2+)-independent release of D-[3H]aspartate that is mediated predominantly by activation of excitatory amino acid receptors resulting in a reversal of the high-affinity dicarboxylic amino acid transport system. Although the physiological relevance of such non-vesicular release from the cytosol remains obscure and is still a matter of some debate, this mode of release may be of pathological significance.
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Affiliation(s)
- J Dunlop
- Department of Biochemistry and Microbiology, University of St. Andrews, Fife, Scotland, U.K
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4
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Sanders MM, Kon C. Glutamine and glutamate metabolism in normal and heat shock conditions inDrosophila Kc cells: Conditions supporting glutamine synthesis maximize heat shock polypeptide expression. J Cell Physiol 1992; 150:620-31. [PMID: 1347046 DOI: 10.1002/jcp.1041500323] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We have previously reported that Drosophila Kc cells require glutamine for maximal expression of heat shock proteins in stressed conditions (Sanders and Kon: J. Cell. Physiol. 146:180-190, 1991). The mechanism of this effect has been investigated by comparing the metabolic utilization of glutamine in conditions which support hsp expression with that of glutamate in conditions where up to 100-fold less hsp is synthesized. This comparison showed that free ammonia was generated by cells incubated in the presence of glutamine in 37 degrees C (heat shock) conditions, but not at 25 degrees C, and not in the presence of glutamate in either normal or heat shock conditions. There was no difference in the amount of [14C]O2 generated from either [14C]-labeled amino acid in the tricarboxylic acid cycle, but three- to four-fold more alanine was synthesized in cells incubated in glutamine than in glutamate. Treating the cells with aminotransferase inhibitors to artificially increase NH3 release raised hsp expression in the presence of glutamate to maximal levels characteristic of glutamine. This potentiation correlated with inhibition of alanine aminotransferase. Since only NH3 production correlated with hsp expression in heat shock conditions in the presence of glutamine, and NH3 addition to glutamate also resulted in maximal hsp expression, we measured glutamine production in glutamate plus NH3 and observed net glutamine synthesis. The supposition that glutamine itself is responsible for the regulatory changes supporting maximal hsp expression was supported by the finding that the glutamine analog, 6-diazo-5-oxo-L-norleucine (DON), mimicked the effects of glutamine. We conclude that glutamine imposes regulatory changes which alter nitrogen metabolism and support hsp expression in Kc cells.
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Affiliation(s)
- M M Sanders
- Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854
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5
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McKenna MC, Tildon JT, Couto R, Stevenson JH, Caprio FJ. The metabolism of malate by cultured rat brain astrocytes. Neurochem Res 1990; 15:1211-20. [PMID: 2129052 DOI: 10.1007/bf01208582] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Since malate is known to play an important role in a variety of functions in the brain including energy metabolism, the transfer of reducing equivalents and possibly metabolic trafficking between different cell types; a series of biochemical determinations were initiated to evaluate the rate of 14CO2 production from L-[U-14C]malate in primary cultures of rat brain astrocytes. The 14CO2 production from labeled malate was almost totally suppressed by the metabolic inhibitors rotenone and antimycin A suggesting that most of malate metabolism was coupled to the electron transport system. A double reciprocal plot of the 14CO2 production from the metabolism of labeled malate revealed biphasic kinetics with two apparent Km and Vmax values suggesting the presence of more than one mechanism of malate metabolism in these cells. Subsequent experiments were carried out using 0.01 mM and 0.5 mM malate to determine whether the addition of effectors would differentially alter the metabolism of high and low concentrations of malate. Effectors studied included compounds which could be endogenous regulators of malate metabolism and metabolic inhibitors which would provide information regarding the mechanisms regulating malate metabolism. Both lactate and aspartate decreased 14CO2 production from 0.01 mM and 0.5 mM malate equally. However, a number of effectors were identified which selectively altered the metabolism of 0.01 mM malate including aminooxyacetate, furosemide, N-acetylaspartate, oxaloacetate, pyruvate and glucose, but had little or no effect on the metabolism of 0.5 mM malate. In addition, alpha-ketoglutarate and succinate decreased 14CO2 production from 0.01 mM malate much more than from 0.5 mM malate. In contrast, a number of effectors altered the metabolism of 0.5 mM malate more than 0.01 mM. These included methionine sulfoximine, glutamate, malonate, alpha-cyano-4-hydroxycinnamate and ouabain. Both the biphasic kinetics and the differential action of many of the effectors on the 14CO2 production from 0.01 mM and 0.5 mM malate provide evidence for the presence of more than one pool of malate metabolism in cultured rat brain astrocytes.
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Affiliation(s)
- M C McKenna
- Department of Pediatrics, University of Maryland School of Medicine Baltimore 21201
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6
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Affiliation(s)
- M Erecińska
- Department of Pharmacology, University of Pennsylvania, School of Medicine, Philadelphia 19104-6084
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Strolin Benedetti M, Cini M, Fusi R, Marrari P, Dostert P. The effects of aging on MAO activity and amino acid levels in rat brain. JOURNAL OF NEURAL TRANSMISSION. SUPPLEMENTUM 1990; 29:259-68. [PMID: 2193110 DOI: 10.1007/978-3-7091-9050-0_25] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The possibility that age-related changes in amino acid levels in various rat brain areas might correlate with modifications of monoamine oxidase (MAO) activity, already found with aging, has been examined. Taurine, aspartic acid and glutamic acid levels were found to be unchanged or decreased with age, whereas GABA and glutamine concentrations increased or remained unchanged. Serine and glycine (except in pons-medulla) levels were found to be unaffected by age. The increase in total MAO activity with aging in some brain areas might contribute to the changes in amino acid levels. Likewise, the possible influence of age-induced changes in activity of various enzymes involved in H2O2 and NH3 detoxication and in amino acid biosynthesis on rat brain amino acid levels are considered. Oral administration of clorgyline or 1-deprenyl to young rats did not significantly modify the concentrations of most brain amino acids.
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Bender AS, Woodbury DM, White HS. Beta-DL-methylene-aspartate, an inhibitor of aspartate aminotransferase, potently inhibits L-glutamate uptake into astrocytes. Neurochem Res 1989; 14:641-6. [PMID: 2571095 DOI: 10.1007/bf00964873] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
[3H]Glutamate uptake into astrocytes in primary culture was potently inhibited by the aspartate analogues L- and D-aspartic acid, DL-threo-beta-hydroxy-aspartic acid-beta-hydroxymate (IC50's: 136, 259, 168, and 560 microM, respectively) and by beta-DL-methylene-aspartate, a suicide inhibitor of aspartate aminotransferase (IC50: 524 microM), and by the endogenous sulphur-containing amino acid L-cysteinesulfinic acid (IC50: 114 microM), [3H]Glutamate uptake was not significantly affected by either N-methyl-D-aspartate or DL-homocysteine thiolactone. These results demonstrate that other excitatory amino acids including aspartate and L-cysteinesulfinic acid (but excluding L-homocysteic acid) interact with the glutamate transport system of astrocytes. Inhibition of glutamate uptake may significantly increase the level of neuronal excitability.
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Affiliation(s)
- A S Bender
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, Salt Lake City 84112
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Lai JC, Murthy CR, Cooper AJ, Hertz E, Hertz L. Differential effects of ammonia and beta-methylene-DL-aspartate on metabolism of glutamate and related amino acids by astrocytes and neurons in primary culture. Neurochem Res 1989; 14:377-89. [PMID: 2569676 DOI: 10.1007/bf01000042] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The effects of ammonium chloride (3 mM) and beta-methylene-DL-aspartate (BMA; 5 mM) (an inhibitor of aspartate aminotransferase, a key enzyme of the malate-aspartate shuttle (MAS] on the metabolism of glutamate and related amino acids were studied in primary cultures of astrocytes and neurons. Both ammonia and BMA inhibited 14CO2 production from [U-14C]- and [1-14C]glutamate by astrocytes and neurons and their effects were partially additive. Acute treatment of astrocytes with ammonia (but not BMA) increased astrocytic glutamine. Acute treatment of astrocytes with ammonia or BMA decreased astrocytic glutamate and aspartate (both are key components of the MAS). Acute treatment of neurons with ammonia decreased neuronal aspartate and glutamine and did not apparently affect the efflux of aspartate from neurons. However, acute BMA treatment of neurons led to decreased neuronal glutamate and glutamine and apparently reduced the efflux of aspartate and glutamine from neurons. The data are consistent with the notion that both ammonia and BMA may inhibit the MAS although BMA may also directly inhibit cellular glutamate uptake. Additionally, these results also suggest that ammonia and BMA exert differential effects on astroglial and neuronal glutamate metabolism.
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Affiliation(s)
- J C Lai
- Department of Biochemistry, Cornell University Medical College, New York, NY 10021
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10
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Affiliation(s)
- R J Huxtable
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson 85724
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11
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Chapman AG, Hart GP. Anticonvulsant drug action and regional neurotransmitter amino acid changes. J Neural Transm (Vienna) 1988; 72:201-12. [PMID: 2901457 DOI: 10.1007/bf01243420] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The role played by the inhibitory transmitters, GABA, glycine and taurine, and by excitatory (aspartate/glutamate) antagonists in mediating anticonvulsant action will be documented. This study provides examples of one anticonvulsant compound that affects glycine metabolism (milacemide), and another that affects aspartate metabolism (beta-methylene-aspartate). Beta-Methylene-aspartate, a selective inhibitor of glutamate-aspartate transaminase activity, protects against sound-induced seizures in audiogenic DBA/2 mice, with an ED50 value of 1.9 mumoles (icv; clonic phase). Forebrain and cerebellar aspartate, glutamate and GABA levels are reduced by 15-30% following the administration of beta-methylene-aspartate. Milacemide, a glycinamide derivative with experimental and clinical anticonvulsant activity, is ineffective against sound-induced seizures in DBA/2 mice. Following the ip administration of milacemide (100 mg/kg; 3 hours) there were significant increases in rat brain glycine levels in the cerebellum (+137%), cortex (+45%) and hippocampus (+59%).
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Affiliation(s)
- A G Chapman
- Department of Neurology, Institute of Psychiatry, London, England
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12
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Cheeseman AJ, Clark JB. Influence of the malate-aspartate shuttle on oxidative metabolism in synaptosomes. J Neurochem 1988; 50:1559-65. [PMID: 3361310 DOI: 10.1111/j.1471-4159.1988.tb03044.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
beta-Methyleneaspartate, a specific inhibitor of aspartate aminotransferase (EC 2.6.1.1.), was used to investigate the role of the malate-aspartate shuttle in rat brain synaptosomes. Incubation of rat brain cytosol, "free" mitochondria, synaptosol, and synaptic mitochondria, with 2 mM beta-methyleneaspartate resulted in inhibition of aspartate aminotransferase by 69%, 67%, 49%, and 76%, respectively. The reconstituted malate-aspartate shuttle of "free" brain mitochondria was inhibited by a similar degree (53%). As a consequence of the inhibition of the aspartate aminotransferase, and hence the malate-aspartate shuttle, the following changes were observed in synaptosomes: decreased glucose oxidation via the pyruvate dehydrogenase reaction and the tricarboxylic acid cycle; decreased acetylcholine synthesis; and an increase in the cytosolic redox state, as measured by the lactate/pyruvate ratio. The main reason for these changes can be attributed to decreased carbon flow through the tricarboxylic acid cycle (i.e., decreased formation of oxaloacetate), rather than as a direct consequence of changes in the NAD+/NADH ratio. Malate/glutamate oxidation in "free" mitochondria was also decreased in the presence of 2 mM beta-methyleneaspartate. This is probably a result of decreased glutamate transport into mitochondria as a result of low levels of aspartate, which are needed for the exchange with glutamate by the energy-dependent glutamate-aspartate translocator.
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Affiliation(s)
- A J Cheeseman
- Department of Biochemistry, Medical College, St. Bartholomew's Hospital, University of London, England
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Abstract
Active site titration provides a means of calibrating enzyme reference materials in molecular concentration units independent from the incubation conditions used in kinetic assays. Such reference materials may serve as primary standards for calibrating any kinetic assay using the same active site. Active site titration of aspartate aminotransferase has been done by fluorimetric measurement of the half-cycle transamination of the phosphopyridoxal form. Another promising approach is the stoichiometric titration with specific suicide substrates such as vinylglycine. Expression of results in molecular concentration units requires that both the primary enzyme standard and the enzyme as measured in blood plasma show similar turnover numbers and substrate specificity in the kinetic assay being used. This is best achieved with purified reference materials of human origin. If the assay in plasma measures the sum of several isoenzymes having different turnover numbers, then the calibration is no longer absolute but becomes method-dependent.
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Affiliation(s)
- M Roth
- Central Laboratory of Clinical Chemistry, University Hospital, Geneva, Switzerland
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Weinstein CL, Griffith OW. Cysteinesulfonate and beta-sulfopyruvate metabolism. Partitioning between decarboxylation, transamination, and reduction pathways. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68986-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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15
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Unsaturated amino acids: Synthesis of trans-3,4-didehydro analogues of L-ornithine and L-arginine. Tetrahedron Lett 1988. [DOI: 10.1016/s0040-4039(00)82302-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Lai JC, Cooper AJ. Brain alpha-ketoglutarate dehydrogenase complex: kinetic properties, regional distribution, and effects of inhibitors. J Neurochem 1986; 47:1376-86. [PMID: 3760866 DOI: 10.1111/j.1471-4159.1986.tb00768.x] [Citation(s) in RCA: 245] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The substrate and cofactor requirements and some kinetic properties of the alpha-ketoglutarate dehydrogenase complex (KGDHC; EC 1.2.4.2, EC 2.3.1.61, and EC 1.6.4.3) in purified rat brain mitochondria were studied. Brain mitochondrial KGDHC showed absolute requirement for alpha-ketoglutarate, CoA and NAD, and only partial requirement for added thiamine pyrophosphate, but no requirement for Mg2+ under the assay conditions employed in this study. The pH optimum was between 7.2 and 7.4, but, at pH values below 7.0 or above 7.8, KGDHC activity decreased markedly. KGDHC activity in various brain regions followed the rank order: cerebral cortex greater than cerebellum greater than or equal to midbrain greater than striatum = hippocampus greater than hypothalamus greater than pons and medulla greater than olfactory bulb. Significant inhibition of brain mitochondrial KGDHC was noted at pathological concentrations of ammonia (0.2-2 mM). However, the purified bovine heart KGDHC and KGDHC activity in isolated rat heart mitochondria were much less sensitive to inhibition. At 5 mM both beta-methylene-D,L-aspartate and D,L-vinylglycine (inhibitors of cerebral glucose oxidation) inhibited the purified heart but not the brain mitochondrial enzyme complex. At approximately 10 microM, calcium slightly stimulated (by 10-15%) the brain mitochondrial KGDHC. At concentrations above 100 microM, calcium (IC50 = 1 mM) inhibited both brain mitochondrial and purified heart KGDHC. The present results suggest that some of the kinetic properties of the rat brain mitochondrial KGDHC differ from those of the purified bovine heart and rat heart mitochondrial enzyme complexes. They also suggest that the inhibition of KGDHC by ammonia and the consequent effect on the citric acid cycle fluxes may be of pathophysiological and/or pathogenetic importance in hyperammonemia and in diseases (e.g., hepatic encephalopathy, inborn errors of urea metabolism, Reye's syndrome) where hyperammonemia is a consistent feature. Brain accumulation of calcium occurs in a number of pathological conditions. Therefore, it is possible that such a calcium accumulation may have a deleterious effect on KGDHC activity.
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Cooper AJ, Haber MT, Ginos JZ, Kaufman P, Kaufman C, Paik YH, Dowd P. Interaction of soluble pig heart glutamate-aspartate transaminase with various beta,gamma-unsaturated amino acids. Biochem Biophys Res Commun 1985; 129:193-9. [PMID: 2860902 DOI: 10.1016/0006-291x(85)91421-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
beta-Ethylidene-DL-aspartate (beta EA) and beta-methylene-DL-glutamate (beta MG) were synthesized and tested as potential suicide inhibitors of soluble pig heart glutamate-aspartate transaminase (sGAT). beta MG was found to be a) a substrate with a very low turnover number relative to glutamate and b) a competitive inhibitor with respect to aspartate (albeit with a large binding constant). At high concentrations beta MG inactivated the enzyme but only very slowly. beta EA was also found to be a substrate with a very low turnover number; it did not inactivate the enzyme (1 hr, 25 degrees C) even at a high concentration. However, beta EA was found to bind to the enzyme with an affinity comparable to that of aspartate and glutamate. beta-Methylene-DL-aspartate (beta MA) has been shown to rapidly inactivate glutamate-aspartate transaminase. Therefore, it appears that glutamate-aspartate transaminase can bind analogues of aspartate with alkene groups in the beta position. The conjugated carbonyl groups of beta MA and beta EA will enhance Michael addition in comparison with that expected for vinylglycine. On the other hand, the presence of the methyl groups should reduce the electrophilicity of the double bond of beta EA compared to beta MA. This deactivation and/or steric hindrance to Michael attack may account for the inability of beta EA to inactivate sGAT. Therefore, it may be possible to design selective suicide inhibitors of glutamate-aspartate++ transaminase with the following structure: HO2CC(= CHX)CH(CO2H)NH2, where X is an electron-withdrawing group. Ideally, X would increase the reactivity of the double bond while affording a minimum of steric hindrance to susceptible enzyme-bound bases.
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Abstract
Aminotransferases are ubiquitous enzymes of mammalian cells and several are of important diagnostic use. The application of aspartate aminotransferase activity measurements in serum from individuals suffering from myocardial infarction brought about a new dimension in clinical laboratory testing in the 1950s. This review focuses on measurement techniques for aspartate aminotransferase and their application (a subsequent article will review other aminotransferases). Assay techniques measuring enzyme activity are direct spectrophotometric measurements, manometric techniques, assays using dye substances, coupled enzyme techniques, and radiometric procedures. Of these procedures, the one employing malate dehydrogenase and NADH is the most important and is covered in particular detail. The estimation of the mitochondrial isoenzyme of aspartate aminotransferase is also of clinical interest, in particular for estimating severity of disease or in specific applications (e.g., chronic alcoholism). Methods reviewed for estimation of this enzyme are electrophoresis, chromatography, differential kinetic behavior, and immunochemical separation. Determination of the enzyme protein by techniques independent of its catalytic activity are also reviewed.
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Fitzpatrick SM, Cooper AJ, Duffy TE. Use of beta-methylene-D,L-aspartate to assess the role of aspartate aminotransferase in cerebral oxidative metabolism. J Neurochem 1983; 41:1370-83. [PMID: 6619872 DOI: 10.1111/j.1471-4159.1983.tb00835.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Several inhibitors of aspartate aminotransferase, a key enzyme of the malate-aspartate shuttle, were investigated for their effects on cerebral oxidative metabolism in vitro. beta-Methylene-D,L-aspartate (2 mM), aminooxyacetate (0.1 mM), and D,L-vinylglycine (20 mM) all significantly reduced the activity of aspartate aminotransferase and the rate of oxygen consumption of rat cerebral cortex slices respiring on glucose. In the presence of beta-methyleneaspartate, a one-to-one correlation was found between the degree of inhibition of tissue respiration and the degree of inhibition of transaminase activity. Slices of rat liver incubated in the presence of glucose and beta-methyleneaspartate showed a similar one-to-one relationship between inhibition of oxygen comsumption and inhibition of aspartate aminotransferase activity, whereas with rat kidney cortex slices, the inhibition of aspartate aminotransferase activity was greater than the inhibition of oxygen consumption. Structural analogs of beta-methyleneaspartate (D,L-beta-methyl-D,L-aspartate, gamma-methyl-D,L-glutamate, and alpha-methyl-D,L-didehydroglutamate) that did not inhibit the activity of aspartate aminotransferase similarly did not inhibit the rate of oxygen consumption by cerebral cortex slices. In the presence of beta-methyleneaspartate, pyruvate oxidation by cerebral cortex slices was inhibited to almost the same extent as was glucose oxidation, and the oxidation of succinate was decreased by approximately 20%. The artificial electron acceptor phenazine methosulfate (0.1 mM) only partially overcame the beta-methyleneaspartate-mediated inhibition of respiration with glucose as substrate. The content of ATP and phosphocreatine declined steadily in slices incubated with glucose and beta-methyleneaspartate. At 1 h the concentration of lactate and the lactate/pyruvate ratio, an indicator of the cytoplasmic redox state, increased threefold, whereas the concentrations of malate, citrate, and aspartate decreased. The findings are interpreted in the context of the hypothesis that enzymes common to the malate-aspartate shuttle and the tricarboxylic acid cycle are physically complexed in brain, so that inhibition of aspartate aminotransferase, a component of the complex, impedes the flow of carbon through both metabolic pathways.(ABSTRACT TRUNCATED AT 400 WORDS)
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