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Robert Schwarcz - One of the best experts on this subject based on the ideXlab platform.
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N-Acetylcysteine Inhibits Kynurenine Aminotransferase II.
Neuroscience, 2020Co-Authors: Tonali Blanco-ayala, Korrapati V Sathyasaikumar, J.d. Uys, V. Pérez-de-la-cruz, L.s. Pidugu, Robert SchwarczAbstract:Abstract The tryptophan metabolite kynurenic acid (KYNA) may play an important role in normal and abnormal cognitive processes, most likely by interfering with α7 nicotinic and NMDA receptor function. KYNA is formed from its immediate precursor Kynurenine either by non-enzymatic oxidation or through irreversible transamination by Kynurenine Aminotransferases. In the mammalian brain, Kynurenine Aminotransferase II (KAT II) is the principal enzyme responsible for the neosynthesis of rapidly mobilizable KYNA, and therefore constitutes an attractive target for pro-cognitive interventions. N-acetylcysteine (NAC), a brain-penetrant drug with pro-cognitive efficacy in humans, has been proposed to exert its actions by increasing the levels of the anti-oxidant glutathione (GSH) in the brain. We report here that NAC, but not GSH, inhibits KAT II activity in brain tissue homogenates from rats and humans with IC50 values in the high micromolar to low millimolar range. With similar potency, the drug interfered with the de novo formation of KYNA in rat brain slices, and NAC was a competitive inhibitor of recombinant human KAT II (Ki: 450 μM). Furthermore, GSH failed to S-glutathionylate recombinant human KAT II treated with the dithiocarbamate drug disulfiram. Shown by microdialysis in the prefrontal cortex of rats treated with Kynurenine (50 mg/kg, i.p.), peripheral administration of NAC (500 mg/kg, i.p., 120 and 60 min before the application of Kynurenine) reduced KYNA neosynthesis by ∼50%. Together, these results suggest that NAC exerts its neurobiological effects at least in part by reducing cerebral KYNA formation via KAT II inhibition.
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inhibition of Kynurenine Aminotransferase ii attenuates hippocampus dependent memory deficit in adult rats treated prenatally with Kynurenine
Hippocampus, 2019Co-Authors: Ana Pocivavsek, Greg I Elmer, Robert SchwarczAbstract:A combination of genetic and environmental factors contributes to schizophrenia (SZ), a catastrophic psychiatric disorder with a hypothesized neurodevelopmental origin. Increases in the brain levels of the tryptophan metabolite kynurenic acid (KYNA), an endogenous antagonist of α7 nicotinic acetylcholine and NMDA receptors, have been implicated specifically in the cognitive deficits seen in persons with SZ. Here we evaluated this role of KYNA by adding the KYNA precursor Kynurenine (100 mg/day) to chow fed to pregnant rat dams from embryonic day (ED) 15 to ED 22 (control: ECon; Kynurenine treated: EKyn). Upon termination of the treatment, all rats received normal rodent chow until the animals were evaluated in adulthood (postnatal days 56-85). EKyn treatment resulted in increased extracellular KYNA and reduced extracellular glutamate in the hippocampus, measured by in vivo microdialysis, and caused impairments in hippocampus-dependent learning in adult rats. Acute administration of BFF816, a systemically active inhibitor of Kynurenine Aminotransferase II (KAT II), the major KYNA-synthesizing enzyme in the brain, normalized neurochemistry and prevented contextual memory deficits in adult EKyn animals. Collectively, these results demonstrate that acute inhibition of KYNA neosynthesis can overcome cognitive impairments that arise as a consequence of elevated brain KYNA in early brain development.
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Targeting Kynurenine Aminotransferase II in psychiatric diseases: promising effects of an orally active enzyme inhibitor.
Schizophrenia bulletin, 2014Co-Authors: Masahiro Okuyama, Yasushi Kajii, Ana Pocivavsek, John P Bruno, Robert SchwarczAbstract:Increased brain levels of the tryptophan metabolite kynurenic acid (KYNA) have been linked to cognitive dysfunctions in schizophrenia and other psychiatric diseases. In the rat, local inhibition of Kynurenine Aminotransferase II (KAT II), the enzyme responsible for the neosynthesis of readily mobilizable KYNA in the brain, leads to a prompt reduction in extracellular KYNA levels, and secondarily induces an increase in extracellular glutamate, dopamine, and acetylcholine levels in several brain areas. Using microdialysis in unanesthetized, adult rats, we now show that the novel, systemically active KAT II inhibitor BFF-816, applied orally at 30 mg/kg in all experiments, mimics the effects of local enzyme inhibition. No tolerance was seen when animals were treated daily for 5 consecutive days. Behaviorally, daily injections of BFF-816 significantly decreased escape latency in the Morris water maze, indicating improved performance in spatial and contextual memory. Thus, systemically applied BFF-816 constitutes an excellent tool for studying the neurobiology of KYNA and, in particular, for investigating the mechanisms linking KAT II inhibition to changes in glutamatergic, dopaminergic, and cholinergic function in brain physiology and pathology.
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crystal structure based selective targeting of the pyridoxal 5 phosphate dependent enzyme Kynurenine Aminotransferase ii for cognitive enhancement
Journal of Medicinal Chemistry, 2010Co-Authors: Franca Rossi, Robert Schwarcz, Casazza Valentina, Silvia Garavaglia, Korrapati V Sathyasaikumar, Shinichi Kojima, Keisuke Okuwaki, Shinichiro Ono, Yasushi Kajii, Menico RizziAbstract:Fluctuations in the brain levels of the neuromodulator kynurenic acid may control cognitive processes and play a causative role in several catastrophic brain diseases. Elimination of the pyridoxal 5′-phosphate dependent enzyme Kynurenine Aminotransferase II reduces cerebral kynurenic acid synthesis and has procognitive effects. The present description of the crystal structure of human Kynurenine Aminotransferase II in complex with its potent and specific primary amine-bearing fluoroquinolone inhibitor (S)-(−)-9-(4-aminopiperazin-1-yl)-8-fluoro-3-methyl-6-oxo-2,3-dihydro-6H-1-oxa-3a-azaphenalene-5-carboxylic acid (BFF-122) should facilitate the structure-based development of cognition-enhancing drugs. From a medicinal chemistry perspective our results demonstrate that the issue of inhibitor specificity for highly conserved PLP-dependent enzymes could be successfully addressed.
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astrocytic localization of Kynurenine Aminotransferase ii in the rat brain visualized by immunocytochemistry
Glia, 2007Co-Authors: Paolo Guidetti, Gloria E Hoffman, Miguel Melendezferro, Edson X Albuquerque, Robert SchwarczAbstract:Kynurenic acid (KYNA), a metabolite of the Kynurenine pathway of tryptophan degradation, is a neuroinhibitory agent present in the mammalian brain. Endogenous KYNA preferentially affects the α7 nicotinic acetylcholine (α7nACh) receptor and, possibly, the glycine co-agonist (glycineB) site of the NMDA receptor. Functionally relevant fluctuations in brain KYNA occur under both physiological and pathological conditions, affecting cholinergic and glutamatergic neurotransmission. Kynurenine Aminotransferase II (KAT II), the major biosynthetic enzyme of KYNA in the rat brain, catalyzes the irreversible formation of KYNA from its immediate bioprecursor, Kynurenine. We now purified rat kidney KAT II to homogeneity, generated a polyclonal rabbit anti-rat KAT II antibody, and purified the antibody using routine biochemical methods. The antibody selectively recognized KAT II by Western blot analysis and in immunotitration experiments. Used for immunocytochemistry, the antibody revealed discrete, specific staining of KAT II-positive astrocyte-like cells throughout the adult rat brain. The presence of KAT II in astrocytes was confirmed by double fluorescence immunostaining with an antibody against the astrocyte-specific marker glial fibrillary acidic protein (GFAP). No specific labeling was detected in neurons or microglia. However, KAT II-positive astrocytes were intimately associated with select neuron populations, supporting a neuromodulatory role of KYNA. Intense staining was frequently seen around brain capillaries, with astrocytic end feet contacting the capillary wall. This may explain the rapid access of blood-derived Kynurenine to KAT II-containing astrocytes. The new anti-KAT II antibody should be useful in the further elucidation of the presumed role of KYNA in brain physiology and pathology. © 2006 Wiley-Liss, Inc.
Qian Han - One of the best experts on this subject based on the ideXlab platform.
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Metabolism of Oxalate in Humans: A Potential Role Kynurenine Aminotransferase/Glutamine Transaminase/Cysteine Conjugate Beta-lyase Plays in Hyperoxaluria.
Current medicinal chemistry, 2019Co-Authors: Qian Han, Cihan Yang, Yinai ZhangAbstract:Hyperoxaluria, excessive urinary oxalate excretion, is a significant health problem worldwide. Disrupted oxalate metabolism has been implicated in hyperoxaluria and accordingly, an enzymatic disturbance in oxalate biosynthesis can result in the primary hyperoxaluria. Alanine glyoxylate Aminotransferase-1 and glyoxylate reductase, the enzymes involving glyoxylate (precursor for oxalate) metabolism, have been related to primary hyperoxalurias. Some studies suggest that other enzymes such as glycolate oxidase and alanine glyoxylate Aminotransferase-2 might be associated with primary hyperoxaluria as well, but evidence of a definitive link is not strong between the clinical cases and gene mutations. There are still some idiopathic hyperoxalurias, which require a further study for the etiologies. Some Aminotransferases, particularly Kynurenine Aminotransferases, can convert glyoxylate to glycine. Based on biochemical and structural characteristics, expression level, subcellular localization of some Aminotransferases, a number of them appear able to catalyze the transamination of glyoxylate to glycine more efficiently than alanine glyoxylate Aminotransferase-1. The aim of this minireview is to explore other undermining causes of primary hyperoxaluria and stimulate research toward achieving a comprehensive understanding of underlying mechanisms leading to the disease. Herein, we reviewed all Aminotransferases in the liver for their functions in glyoxylate metabolism. Particularly, Kynurenine Aminotransferase-I and III were carefully discussed regarding their biochemical and structural characteristics, cellular localization, and enzyme inhibition. Kynurenine Aminotransferase-III is, so far, the most efficient putative mitochondrial enzyme to transaminate glyoxylate to glycine in mammalian livers, might be an interesting enzyme to look over in hyperoxaluria etiology of primary hyperoxaluria and should be carefully investigated for its involvement in oxalate metabolism.
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Biochemical and structural characterization of mouse mitochondrial aspartate Aminotransferase, a newly identified Kynurenine Aminotransferase-IV.
Bioscience reports, 2011Co-Authors: Qian Han, Tao Cai, Howard Robinson, Danilo A. TagleAbstract:Mammalian mAspAT (mitochondrial aspartate Aminotransferase) is recently reported to have KAT (Kynurenine Aminotransferase) activity and plays a role in the biosynthesis of KYNA (kynurenic acid) in rat, mouse and human brains. This study concerns the biochemical and structural characterization of mouse mAspAT. In this study, mouse mAspAT cDNA was amplified from mouse brain first stand cDNA and its recombinant protein was expressed in an Escherichia coli expression system. Sixteen oxo acids were tested for the co-substrate specificity of mouse mAspAT and 14 of them were shown to be capable of serving as co-substrates for the enzyme. Structural analysis of mAspAT by macromolecular crystallography revealed that the cofactor-binding residues of mAspAT are similar to those of other KATs. The substrate-binding residues of mAspAT are slightly different from those of other KATs. Our results provide a biochemical and structural basis towards understanding the overall physiological role of mAspAT in vivo and insight into controlling the levels of endogenous KYNA through modulation of the enzyme in the mouse brain.
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Structural Insight into the Inhibition of Human Kynurenine Aminotransferase I/Glutamine Transaminase K
Journal of medicinal chemistry, 2009Co-Authors: Qian Han, Tao Cai, Howard Robinson, Danilo A. TagleAbstract:Human Kynurenine Aminotransferase I (hKAT I) catalyzes the formation of kynurenic acid, a neuroactive compound. Here, we report three high-resolution crystal structures (1.50-1.55 A) of hKAT I that are in complex with glycerol and each of two inhibitors of hKAT I: indole-3-acetic acid (IAC) and Tris. Because Tris is able to occupy the substrate binding position, we speculate that this may be the basis for hKAT I inhibition. Furthermore, the hKAT/IAC complex structure reveals that the binding moieties of the inhibitor are its indole ring and a carboxyl group. Six chemicals with both binding moieties were tested for their ability to inhibit hKAT I activity; 3-indolepropionic acid and DL-indole-3-lactic acid demonstrated the highest level of inhibition, and as they cannot be considered as substrates of the enzyme, these two inhibitors are promising candidates for future study. Perhaps even more significantly, we report the discovery of two different ligands located simultaneously in the hKAT I active center for the first time.
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Biochemical and structural properties of mouse Kynurenine Aminotransferase III.
Molecular and cellular biology, 2008Co-Authors: Qian Han, Tao Cai, Howard Robinson, Danilo A. TagleAbstract:Kynurenine Aminotransferase III (KAT III) has been considered to be involved in the production of mammalian brain kynurenic acid (KYNA), which plays an important role in protecting neurons from overstimulation by excitatory neurotransmitters. The enzyme was identified based on its high sequence identity with mammalian KAT I, but its activity toward Kynurenine and its structural characteristics have not been established. In this study, the biochemical and structural properties of mouse KAT III (mKAT III) were determined. Specifically, mKAT III cDNA was amplified from a mouse brain cDNA library, and its recombinant protein was expressed in an insect cell protein expression system. We established that mKAT III is able to efficiently catalyze the transamination of Kynurenine to KYNA and has optimum activity at relatively basic conditions of around pH 9.0 and at relatively high temperatures of 50 to 60°C. In addition, mKAT III is active toward a number of other amino acids. Its activity toward Kynurenine is significantly decreased in the presence of methionine, histidine, glutamine, leucine, cysteine, and 3-hydroxyKynurenine. Through macromolecular crystallography, we determined the mKAT III crystal structure and its structures in complex with Kynurenine and glutamine. Structural analysis revealed the overall architecture of mKAT III and its cofactor binding site and active center residues. This is the first report concerning the biochemical characteristics and crystal structures of KAT III enzymes and provides a basis toward understanding the overall physiological role of mammalian KAT III in vivo and insight into regulating the levels of endogenous KYNA through modulation of the enzyme in the mouse brain.
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Substrate specificity and structure of human aminoadipate Aminotransferase/Kynurenine Aminotransferase II.
Bioscience reports, 2008Co-Authors: Qian Han, Tao Cai, Danilo A. Tagle, Howard RobinsonAbstract:Aminotransferase, capable of catalysing the transamination of Kynurenine to KYNA (kynurenic acid), has commonly been termed KAT (Kynurenine Aminotransferase). KYNA is the only known endogenous antagonist of the NMDA (N-methyl-d-aspartate) subtype of glutamate receptors [1-4]. KYNA is also the antagonist of the α7-nicotinic acetylcholine receptor [5-8]. The level of KYNA is altered in several neurodegenerative diseases, including Huntington’s disease [9,10], Alzheimer’s disease [11], schizophrenia [12-14] and acquired immunodeficiency syndrome dementia [15]. Because KYNA must be produced by KAT-catalysed Kynurenine transamination, Aminotransferases, responsible for catalysing Kynurenine to KYNA, have been considered to be targets for maintaining and regulating physiological concentrations of brain KYNA. In humans, rats and mice, four enzymes, KAT I, II, III and IV, are considered to be involved in KYNA synthesis in the central nervous system [16-21]. Of these, KAT I and KAT II have been extensively studied and the crystal structures of hKAT I (human Kynurenine Aminotransferase I) and hKAT II (human Kynurenine Aminotransferase II) are now available [16,17,19,22-25]. It has been reported that KAT I has a broad substrate specificity and displays maximum activity at relatively basic conditions. This poses critical questions regarding the contribution of KAT I to brain KYNA production [16,17]. On the other hand, KAT II is identical to AADAT (aminoadipate Aminotransferase) and catalyses the transamination of Kynurenine and aminoadipate and is localized in the soluble cytoplasm [16]. The enzyme has been cloned from both rats and humans and its presence in the brain has been confirmed by Northern and Western blotting [26-29]. Previous studies on KAT II/AADAT have been focused on its activity on aminoadipate in peripheral organs, especially in the liver and the kidney, and on its role in brain KYNA production [30-32]. Although there have been a number of studies addressing the biochemical characterization of KAT II/AADAT, the overall substrate specificity and kinetic properties have not been clearly established for KAT II from any species. In the present study, we determined its overall substrate profile, kinetic parameters and the complex structure of hKAT II with α-oxoglutaric acid. The present study shows a novel biochemical characterization of hKAT II.
Etsuo Okuno - One of the best experts on this subject based on the ideXlab platform.
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presence of l Kynurenine Aminotransferase iii in retinal ganglion cells and corpora amylacea in the human retina and optic nerve
Folia Neuropathologica, 2011Co-Authors: Robert Rejdak, Etsuo Okuno, Eberhart Zrenner, C Rummelt, Pawel Grieb, Konrad Rejdak, Sebastian Thaler, Katarzyna Nowomiejska, Friedrich E Kruse, Waldemar A. TurskiAbstract:Background: Corpora amylacea (CAm) are a hallmark of aging and neurodegeneration. The presence of Kynurenine Aminotransferases I and II (KAT I and II) in CAm in the human retina and optic nerve has been already shown. The pre - sent study aimed to examine Kynurenine Aminotransferase III (KAT III) immunoreactivity in CAm in the human reti - na and optic nerve. Material and methods: Polyclonal antibody against KAT III was used on sections of human eyes enucleated due to malignant uveal melanoma. PAS-stained sections of CAm were compared with KAT III stained ones. Results: KAT III immunoreactivity was observed in CAm in the retina, prelaminar, laminar and retrolaminar region of the optic nerve with similar location to PAS-stained sections. The most intense staining was observed in the retro - laminar part of the optic nerve. KAT III immunoreactivity was also present in the cytoplasm of retinal ganglion cells. Conclusions: Expression of KAT III in CAm in the human retina and optic nerve indicates that this enzyme may be relevant in mechanisms of neurodegeneration leading to CAm formation.
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Presence of L-Kynurenine Aminotransferase III in retinal ganglion cells and corpora amylacea in the human retina and optic nerve.
Folia neuropathologica, 2011Co-Authors: Robert Rejdak, Etsuo Okuno, Eberhart Zrenner, C Rummelt, Pawel Grieb, Konrad Rejdak, Sebastian Thaler, Katarzyna Nowomiejska, Friedrich E Kruse, Waldemar A. TurskiAbstract:Background: Corpora amylacea (CAm) are a hallmark of aging and neurodegeneration. The presence of Kynurenine Aminotransferases I and II (KAT I and II) in CAm in the human retina and optic nerve has been already shown. The pre - sent study aimed to examine Kynurenine Aminotransferase III (KAT III) immunoreactivity in CAm in the human reti - na and optic nerve. Material and methods: Polyclonal antibody against KAT III was used on sections of human eyes enucleated due to malignant uveal melanoma. PAS-stained sections of CAm were compared with KAT III stained ones. Results: KAT III immunoreactivity was observed in CAm in the retina, prelaminar, laminar and retrolaminar region of the optic nerve with similar location to PAS-stained sections. The most intense staining was observed in the retro - laminar part of the optic nerve. KAT III immunoreactivity was also present in the cytoplasm of retinal ganglion cells. Conclusions: Expression of KAT III in CAm in the human retina and optic nerve indicates that this enzyme may be relevant in mechanisms of neurodegeneration leading to CAm formation.
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Kynurenine Aminotransferase in the supratentorial dura mater of the rat: effect of stimulation of the trigeminal ganglion
Experimental neurology, 2004Co-Authors: Elizabeth Knyihár-csillik, Etsuo Okuno, József Toldi, Zoltán Chadaide, Beáta Krisztin-péva, Csaba Varga, Andor H. Molnár, Bert Csillik, László VécseiAbstract:Electrical stimulation of the trigeminal ganglion has been widely used as a model of nociception, characterizing migraine. This treatment is known to evoke release of neuropeptides and neurotransmitters from nerve fibers of the dura mater. On the basis of immunocytochemical investigations, we found that under normal conditions, surface membranes of Schwann cells surrounding nerve fibers in the supratentorial dura mater display Kynurenine Aminotransferase-immunoreaction (KAT-IR); also KAT-IR are the granules of mast cells and the cytoplasms of macrophages (histiocytes). In consequence of stimulation of the trigeminal ganglion, Schwann cells in the dura mater became conspicuously swollen while their KAT-IR decreased considerably; also KAT-IR of mast cells and macrophages decreased significantly. At the same time, nitric oxide synthase (NOS)-IR of nerve fibers in the dura mater increased, suggesting release of nitric oxide (NO), this is known to be involved in NMDA receptor activation leading to vasodilation followed by neurogenic inflammation. Because kynurenic acid (KYNA) is an antagonist of NMDA receptors, we hypothesize that KYNA and its synthesizing enzyme, KAT, may play a role in the prevention of migraine attacks.
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Ontogenic changes of Kynurenine Aminotransferase I activity and its expression in the chicken retina
Vision research, 2003Co-Authors: Robert Rejdak, Etsuo Okuno, Elzbieta Zielinska, Yana Shenk, Waldemar A. Turski, Tomasz Zarnowski, Zbigniew Zagórski, Eberhart Zrenner, Konrad KohlerAbstract:Kynurenine Aminotransferases are key enzymes for the synthesis of kynurenic acid (KYNA), an endogenous glutamate receptor antagonist. The study described here examined ontogenic changes of Kynurenine Aminotransferase I (KAT I) activity and its expression in the chicken retina. KAT I activity measured on embryonic day 16 (E16) was significantly higher than at all other stages (E12, P0 and P7). Double labeling with antibodies against glutamine synthetase showed that on P7 KAT I was expressed in Muller cell endfeet and their processes in the inner retina. Since KAT I activity is high in the late embryonic stages, it is conceivable that it plays a neuromodulatory role in the retina during the late phase of embryogenesis.
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Effects of in vivo sodium azide administration on the immunohistochemical localization of Kynurenine Aminotransferase in the rat brain.
Neuroscience, 1999Co-Authors: Elizabeth Knyihár-csillik, Etsuo Okuno, László VécseiAbstract:Endogenous excitotoxins that act on receptors of cerebral excitatory amino acids play important roles in the pathogenesis of excitotoxic brain diseases. Activation of excitatory amino acid receptors results in neuronal death characteristic of these disorders. Kynurenic acid, a powerful endogenous excitatory amino acid receptor antagonist, which is therefore widely regarded as a potent neuroprotective agent, is produced from its biological precursor, L-Kynurenine, by the action of the enzyme Kynurenine Aminotransferase-I. The chemical hypoxia induced by mitochondrial toxins produces a secondary excitotoxicity, leading to the activation of N-methyl-D-aspartate receptors. Accordingly, sodium azide, an inhibitor of cytochrome oxidase, induces the release of excitotoxins via an energy impairment and this, in turn, results in neurodegeneration. Since energy-dependent secondary excitotoxic mechanisms also account for the pathogenesis of neurodegenerative diseases, a study was made of the effects of sodium azide on the immunohistochemical localization of Kynurenine Aminotransferase-I. After in vivo administration of sodium azide for five days, a markedly decreased glial Kynurenine Aminotransferase-I immunoreactivity was found by immunohistochemical techniques in the glial cells of the striatum, hippocampus, dentate gyrus and temporal cortex; at the same time, Kynurenine Aminotransferase-I started to be expressed by nerve cells which had not been immunoreactive previously. The accumulation of Kynurenine Aminotransferase-I reaction product around the ribosomes of neuronal endoplasmic reticulum suggests de novo synthesis of Kynurenine Aminotransferase-I in the reactive nerve cells.
Howard Robinson - One of the best experts on this subject based on the ideXlab platform.
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Biochemical and structural characterization of mouse mitochondrial aspartate Aminotransferase, a newly identified Kynurenine Aminotransferase-IV.
Bioscience reports, 2011Co-Authors: Qian Han, Tao Cai, Howard Robinson, Danilo A. TagleAbstract:Mammalian mAspAT (mitochondrial aspartate Aminotransferase) is recently reported to have KAT (Kynurenine Aminotransferase) activity and plays a role in the biosynthesis of KYNA (kynurenic acid) in rat, mouse and human brains. This study concerns the biochemical and structural characterization of mouse mAspAT. In this study, mouse mAspAT cDNA was amplified from mouse brain first stand cDNA and its recombinant protein was expressed in an Escherichia coli expression system. Sixteen oxo acids were tested for the co-substrate specificity of mouse mAspAT and 14 of them were shown to be capable of serving as co-substrates for the enzyme. Structural analysis of mAspAT by macromolecular crystallography revealed that the cofactor-binding residues of mAspAT are similar to those of other KATs. The substrate-binding residues of mAspAT are slightly different from those of other KATs. Our results provide a biochemical and structural basis towards understanding the overall physiological role of mAspAT in vivo and insight into controlling the levels of endogenous KYNA through modulation of the enzyme in the mouse brain.
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Structural Insight into the Inhibition of Human Kynurenine Aminotransferase I/Glutamine Transaminase K
Journal of medicinal chemistry, 2009Co-Authors: Qian Han, Tao Cai, Howard Robinson, Danilo A. TagleAbstract:Human Kynurenine Aminotransferase I (hKAT I) catalyzes the formation of kynurenic acid, a neuroactive compound. Here, we report three high-resolution crystal structures (1.50-1.55 A) of hKAT I that are in complex with glycerol and each of two inhibitors of hKAT I: indole-3-acetic acid (IAC) and Tris. Because Tris is able to occupy the substrate binding position, we speculate that this may be the basis for hKAT I inhibition. Furthermore, the hKAT/IAC complex structure reveals that the binding moieties of the inhibitor are its indole ring and a carboxyl group. Six chemicals with both binding moieties were tested for their ability to inhibit hKAT I activity; 3-indolepropionic acid and DL-indole-3-lactic acid demonstrated the highest level of inhibition, and as they cannot be considered as substrates of the enzyme, these two inhibitors are promising candidates for future study. Perhaps even more significantly, we report the discovery of two different ligands located simultaneously in the hKAT I active center for the first time.
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Biochemical and structural properties of mouse Kynurenine Aminotransferase III.
Molecular and cellular biology, 2008Co-Authors: Qian Han, Tao Cai, Howard Robinson, Danilo A. TagleAbstract:Kynurenine Aminotransferase III (KAT III) has been considered to be involved in the production of mammalian brain kynurenic acid (KYNA), which plays an important role in protecting neurons from overstimulation by excitatory neurotransmitters. The enzyme was identified based on its high sequence identity with mammalian KAT I, but its activity toward Kynurenine and its structural characteristics have not been established. In this study, the biochemical and structural properties of mouse KAT III (mKAT III) were determined. Specifically, mKAT III cDNA was amplified from a mouse brain cDNA library, and its recombinant protein was expressed in an insect cell protein expression system. We established that mKAT III is able to efficiently catalyze the transamination of Kynurenine to KYNA and has optimum activity at relatively basic conditions of around pH 9.0 and at relatively high temperatures of 50 to 60°C. In addition, mKAT III is active toward a number of other amino acids. Its activity toward Kynurenine is significantly decreased in the presence of methionine, histidine, glutamine, leucine, cysteine, and 3-hydroxyKynurenine. Through macromolecular crystallography, we determined the mKAT III crystal structure and its structures in complex with Kynurenine and glutamine. Structural analysis revealed the overall architecture of mKAT III and its cofactor binding site and active center residues. This is the first report concerning the biochemical characteristics and crystal structures of KAT III enzymes and provides a basis toward understanding the overall physiological role of mammalian KAT III in vivo and insight into regulating the levels of endogenous KYNA through modulation of the enzyme in the mouse brain.
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Substrate specificity and structure of human aminoadipate Aminotransferase/Kynurenine Aminotransferase II.
Bioscience reports, 2008Co-Authors: Qian Han, Tao Cai, Danilo A. Tagle, Howard RobinsonAbstract:Aminotransferase, capable of catalysing the transamination of Kynurenine to KYNA (kynurenic acid), has commonly been termed KAT (Kynurenine Aminotransferase). KYNA is the only known endogenous antagonist of the NMDA (N-methyl-d-aspartate) subtype of glutamate receptors [1-4]. KYNA is also the antagonist of the α7-nicotinic acetylcholine receptor [5-8]. The level of KYNA is altered in several neurodegenerative diseases, including Huntington’s disease [9,10], Alzheimer’s disease [11], schizophrenia [12-14] and acquired immunodeficiency syndrome dementia [15]. Because KYNA must be produced by KAT-catalysed Kynurenine transamination, Aminotransferases, responsible for catalysing Kynurenine to KYNA, have been considered to be targets for maintaining and regulating physiological concentrations of brain KYNA. In humans, rats and mice, four enzymes, KAT I, II, III and IV, are considered to be involved in KYNA synthesis in the central nervous system [16-21]. Of these, KAT I and KAT II have been extensively studied and the crystal structures of hKAT I (human Kynurenine Aminotransferase I) and hKAT II (human Kynurenine Aminotransferase II) are now available [16,17,19,22-25]. It has been reported that KAT I has a broad substrate specificity and displays maximum activity at relatively basic conditions. This poses critical questions regarding the contribution of KAT I to brain KYNA production [16,17]. On the other hand, KAT II is identical to AADAT (aminoadipate Aminotransferase) and catalyses the transamination of Kynurenine and aminoadipate and is localized in the soluble cytoplasm [16]. The enzyme has been cloned from both rats and humans and its presence in the brain has been confirmed by Northern and Western blotting [26-29]. Previous studies on KAT II/AADAT have been focused on its activity on aminoadipate in peripheral organs, especially in the liver and the kidney, and on its role in brain KYNA production [30-32]. Although there have been a number of studies addressing the biochemical characterization of KAT II/AADAT, the overall substrate specificity and kinetic properties have not been clearly established for KAT II from any species. In the present study, we determined its overall substrate profile, kinetic parameters and the complex structure of hKAT II with α-oxoglutaric acid. The present study shows a novel biochemical characterization of hKAT II.
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substrate specificity and structure of human aminoadipate Aminotransferase Kynurenine Aminotransferase ii
Bioscience Reports, 2008Co-Authors: Qian Han, Tao Cai, Danilo A. Tagle, Howard RobinsonAbstract:Aminotransferase, capable of catalysing the transamination of Kynurenine to KYNA (kynurenic acid), has commonly been termed KAT (Kynurenine Aminotransferase). KYNA is the only known endogenous antagonist of the NMDA (N-methyl-d-aspartate) subtype of glutamate receptors [1-4]. KYNA is also the antagonist of the α7-nicotinic acetylcholine receptor [5-8]. The level of KYNA is altered in several neurodegenerative diseases, including Huntington’s disease [9,10], Alzheimer’s disease [11], schizophrenia [12-14] and acquired immunodeficiency syndrome dementia [15]. Because KYNA must be produced by KAT-catalysed Kynurenine transamination, Aminotransferases, responsible for catalysing Kynurenine to KYNA, have been considered to be targets for maintaining and regulating physiological concentrations of brain KYNA. In humans, rats and mice, four enzymes, KAT I, II, III and IV, are considered to be involved in KYNA synthesis in the central nervous system [16-21]. Of these, KAT I and KAT II have been extensively studied and the crystal structures of hKAT I (human Kynurenine Aminotransferase I) and hKAT II (human Kynurenine Aminotransferase II) are now available [16,17,19,22-25]. It has been reported that KAT I has a broad substrate specificity and displays maximum activity at relatively basic conditions. This poses critical questions regarding the contribution of KAT I to brain KYNA production [16,17]. On the other hand, KAT II is identical to AADAT (aminoadipate Aminotransferase) and catalyses the transamination of Kynurenine and aminoadipate and is localized in the soluble cytoplasm [16]. The enzyme has been cloned from both rats and humans and its presence in the brain has been confirmed by Northern and Western blotting [26-29]. Previous studies on KAT II/AADAT have been focused on its activity on aminoadipate in peripheral organs, especially in the liver and the kidney, and on its role in brain KYNA production [30-32]. Although there have been a number of studies addressing the biochemical characterization of KAT II/AADAT, the overall substrate specificity and kinetic properties have not been clearly established for KAT II from any species. In the present study, we determined its overall substrate profile, kinetic parameters and the complex structure of hKAT II with α-oxoglutaric acid. The present study shows a novel biochemical characterization of hKAT II.
L Liao - One of the best experts on this subject based on the ideXlab platform.
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improvement in detrusor sphincter dyssynergia by bladder wall injection of replication defective herpes simplex virus vector mediated gene delivery of Kynurenine Aminotransferase ii in spinal cord injury rats
Spinal Cord, 2017Co-Authors: Zhaoming Wang, L LiaoAbstract:Improvement in detrusor-sphincter dyssynergia by bladder-wall injection of replication-defective herpes simplex virus vector-mediated gene delivery of Kynurenine Aminotransferase II in spinal cord injury rats
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Herpes simplex virus vector-mediated gene transfer of Kynurenine Aminotransferase improves detrusor overactivity in spinal cord-injured rats
Gene therapy, 2014Co-Authors: C Jia, Naoki Yoshimura, L LiaoAbstract:Herpes simplex virus vector-mediated gene transfer of Kynurenine Aminotransferase improves detrusor overactivity in spinal cord-injured rats
