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 naturally occurring toxin L-2-amino-4-methoxy-trans-3-butenoic (AMB) acid irreversibly inhibits pyridoxal phosphate-linked aspartate aminotransferase. The inhibitor is a substrate for the enzyme, and as such is converted into a highly reactive intermediate which chemically reacts with an active site residue, thus irreversibly inactivating the enzyme. Enzymological and model studies on AMB are presented which enable one to determine the precise mechanism of action of this toxin. The mechanism involves Schiff base formation between the enzyme and toxin followed by alpha-C--H bond cleavage and aldimine isomerization to generate a bifunctional Michael acceptor. This molecule alkylates an active site residue by an addition and elimination route.
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PMID:Mechanism of the irreversible inhibition of aspartate aminotransferase by the bacterial toxin L-2-amino-4-methoxy-trans-3-butenoic acid. 0 51

Intraperitoneal administration to rats of D- or DL-alpha-hydrazinoimidazolylpropionic acid was found to produce a substantial inactivation of hepatic histidine ammonia-lyase (EC 4.3.1.3) in vivo. Proportional to this loss in enzyme activity was an impairment of the ability of treated rats to oxidize L-[ring-2-14C] histidine to 14CO2. Rats in which hepatic histidine ammonia-lyase activity was either depressed by DL-hydrazinoimidazolylproprionic acid injection or elevated by feeding a high protein diet displayed proportionately altered rates of 3H2O release into plasma water following L-[3-3H] histidine administration. Plasma L-histidine clearance following loading with this amino acid was similarly affected by these treatments. Administration of DL-alphal-hydrazinoimisazolylproprionic acid to rats was also found to inactivate non-specifically pyridoxal 5-phosphate enzymes in vivo; pyridoxine injection was found to reverse the DL-alpha-hydrazinoimidazolylproprionic acid-induced inactivation of hepatic aspartate aminotransferase (EC 2.6.1.1) in vivo, but not that of hepatic histidine ammonia-lyase. These findings demonstrate that histidine ammonia-lyase is the rate-limiting factor in L-histidine degradation in the rat. The potential usefulness of DL-hydrazinoimidazolylproprionic acid in the production of an animal model for histidinemia (hereditary histidine ammonia-lyase deficiency) is discussed.
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PMID:Studies on the production and assessment of experimental histidinemia in the rat. 0 33

In previous studies it was found that: (a) aspartate aminotransferase increases the aspartate dehydrogenase activity of glutamate dehydrogenase; (b) the pyridoxamine-P form of this aminotransferase can form an enzyme-enzyme complex with glutamate dehydrogenase; and (c) the pyridoxamine-P form can be dehydrogenated to the pyridoxal-P form by glutamate dehydrogenase. It was therefore concluded (Fahien, L.A., and Smith, S.E. (1974) J. Biol. Chem 249, 2696-2703) that in the aspartate dehydrogenase reaction, aspartate converts the aminotransferase into the pyridoxamine-P form which is then dehydrogenated by glutamate dehydrogenase. The present results support this mechanism and essentially exclude the possibility that aspartate actually reacts with glutamate dehydrogenase and the aminotransferase is an allosteric activator. Indeed, it was found that aspartate is actually an activator of the reaction between glutamate dehydrogenase and the pyridoxamine-P form of the aminotransferase. Aspartate also markedly activated the alanine dehydrogenase reaction catalyzed by glutamate dehydrogenase plus alanine aminotransferase and the ornithine dehydrogenase reaction catalyzed by ornithine aminotransferase plus glutamate dehydrogenase. In these latter two reactions, there is no significant conversion of aspartate to oxalecetate and other compounds tested (including oxalacetate) would not substitute for aspartate. Thus aspartate is apparently bound to glutamate dehydrogenase and this increases the reactivity of this enzyme with the pyridoxamine-P form of aminotransferases. This could be of physiological importance because aspartate enables the aspartate and ornithine dehydrogenase reactions to be catalyzed almost as rapidly by complexes between glutamate dehydrogenase and the appropriate mitochondrial aminotransferase in the absence of alpha-ketoglutarate as they are in the presence of this substrate. Furthermore, in the presence of aspartate, alpha-ketoglutarate can have little or no affect on these reactions. Consequently, in the mitochondria of some organs these reactions could be catalyzed exclusively by enzyme-enzyme complexes even in the presence of alpha-ketoglutarate. Rat liver glutamate dehydrogenase is essentially as active as thebovine liver enzyme with aminotransferases. Since the rat liver enzyme does not polymerize, this unambiguously demonstrates that monomeric forms of glutamate dehydrogenase can react with aminotransferases.
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PMID:Effect of aspartate on complexes between glutamate dehydrogenase and various aminotransferases. 1 47

The selective reaction of Cys-45 and -82, on the one hand, and Cys-390, on the other, with 3-bromo-1,1,1-trifluoropropanone allows for the probing of these regions of aspartate transaminase in the absence and in the presence of enzymatic ligands by 19F nuclear magnetic resonance (NMR). The 19F chemical shifts of the resonance lines differ for the three cysteines and so does their behavior with pH changes. The resonance signals with chemical shifts at 615 and 800 Hz upfield from trifluoroacetic acid correspond to modified cysteine-82 and -45 and have tentatively been assigned in this order. The 615-Hz resonance is affected by pH changes that fit best the influence of a single ionizing residue. On the 800-Hz line, the pH changes appear to be the influence of a minimum of two ionizing residues. The 19F resonance from modified Cys-390 is pH independent in the pH range 5-9 for the pyridoxal phosphate, pyridoxamine phosphate, and apoenzyme forms of the enzyme. Occupation of the active site by a quasi-enzyme-substrate complex, trifluoromethionine pyridoxyl phosphate, affects the 19F chemical shift of modified Cys-390, making it pH dependent with a pK value of 8.4. The 19F NMR properties of the pyridoxal form of Cys-390-modified enzyme can be used to monitor some ligand interactions with the active-center region. Addition of alpha-ketoglutarate or succinate to the ketone labeled enzyme causes a decrease in the resonance line width, and titrations show that this procedure is a good method with which to study the affinity of the enzyme for these ligands. The interpretation of the chemical shift and line-width characteristics of the 19F resonance arising from Cys-390 are most consistent with a model in which the region around this residue seems to be affected by conformational changes arising from substrate binding to the active-center subsites in productive (covalent) manner. Nonproductive complexes which possess fast ligand-protein exchange, such as those between alpha-ketoglutarate or succinate with the pyridoxal phosphate form of the enzyme, may result only in a greater degree of freedom for Cys-390.
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PMID:Fluorine-19 nuclear magnetic resonance studies of effects of ligands on trifluoroacetonylated supernatant aspartate transaminase. 1 84

Difluoro-oxaloacetate interacts with the aldimine form of aspartate transaminase to give a complex, the dissociation constant of which has been determined spectrophotometrically and by 19F n.m.r. (nuclear magnetic resonance). The 19F n.m.r. line-width-pH and chemical-shift-pH profiles of difluoro-oxaloacetate in the presence of the aldimine form of the enzyme both show inflexion points in the pH5 and pH8 regions, which may arise from variations in the binding of difluoro-oxaloacetate as specific groups on the enzyme are successively protonated. Difluoro-oxaloacetate also interacts with apoenzyme to form a complex, the dissociation constant of which was determined by 19F n.m.r. The 19F n.m.r. line-width-pH and chemical-shift-pH profiles of difluoro-oxaloacetate in the presence of apoenzyme show a single inflexion point in the region of pH8. The absence, in this case, of an inflexion in the pH5 region indicates that the latter, present in the corresponding profiles for the aldimine form of the enzyme, results from ionization of an enzyme group associated with the pyridoxal phosphate cofactor.
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PMID:[19F]fluorine nuclear-magnetic-resonance study of the interaction of difluoro-oxaloacetate with aspartate transaminase. 1 99

Amino groups in the pyridoxal phosphate, pyridoxamine phosphate, and apo forms of pig heart cytoplasmic aspartate aminotransferase (L-aspartate: 2-oxoglutarate aminotransferase, EC .2.6.1.1) have been reversibly modified with 2,4-pentanedione. The rate of modification has been measured spectrophotometrically by observing the formation of the enamine produced and this rate has been compared with the rate of loss of catalytic activity for all three forms of the enzyme. Of the 21 amino groups per 46 500 molecular weight, approx. 16 can be modified in the pyridoxal phosphate form with less than a 50% change in the catalytic activity of the enzyme. A slow inactivation occurs which is probably due to reaction of 2,4-pentanedione with the enzyme-bound pyridoxal phosphate. The pyridoxamine phosphate enzyme is completely inactivated by reaction with 2,4-pentanedione. The inactivation of the pyridoxamine phosphate enzyme is not inhibited by substrate analogs. A single lysine residue in the apoenzyme reacts approx. 100 times faster with 2,4-pentanedione than do other amino groups. This lysine is believed to be lysine-258, which forms a Schiff base with pyridoxal phosphate in the holoenzyme.
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PMID:Reversible modification of amino groups in aspartate aminotransferase. 1 99

The activity, properties, and developmental pattern of cysteine sulfinate transaminase (CSA-T) were studied in chick retina and compared with the activity, properties, and developmental pattern of glutamate oxaloacetate transaminase (GOT). Their optimum pH is identical whereas the effect of pyridoxal phosphate seems to be different. Developmental patterns are also different. The Km and Vm of CSA-T and GOT were determined in chick retina homogenate. These results suggest that two different enzymes are responsible for the transamination of cysteine sulfinate (CSA) and aspartate.
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PMID:Comparative study of miscellaneous properties of cysteine sulfinate transaminase and glutamate oxaloacetate transaminase in chick retina homogenate. 2 90

Rose-bengal-sensitized photooxidation of aspartate transaminase from chicken heart cytosol results in a loss of enzymatic activity which follow first order kinetics down to 70--75% inactivation. 0.9 Histidine, 0.9 tryptophane residues and 1.5 SH groups per enzyme subunit were found to be modified in the photooxidized transaminase, which retained 26% residual activity. Photodestruction of the coenzyme was about 16%. The rate of enzyme photoinactivation is constant in the pH range 6--8, and drastically decreases with lowering pH from 6 to 4. alpha-Ketoglutarate partially protects the holoenzyme from inactivation. The apoenzyme undergoes photoinactivation at a rate almost twice as rapid as the holoenzyme. Photooxidized apotransaminase retains affinity to pyridoxal phosphate and binds as much coenzyme as the native apoenzyme. Photooxidation induces no significant alterations in the circular dichroism pattern of the enzyme in the 200 to 240 nm range. However, positive circular dichroism is markedly increased in the absorption bands of aromatic amino acids (260--300 nm). The affinity of photooxidized holoenzyme for glutarate and alpha-methyl aspartate is greatly decreased. On the other hand, photooxidized enzyme retains its ability to bind alpha-alanine and to catalize the transamination half-reaction between alpha-alanine and the bound coenzyme. These findings imply that photooxidation disturbs the binding of the distal carboxyl group of dicarboxylic substrates. This may be due to a localized conformational change induced by destruction of a photoreactive histidine residue at the active site. A role of the histidine residue in transamination reaction is discussed.
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PMID:[Photooxidation of aspartate transaminase from chicken heart cytosol]. 3 52

Two aminotransferases from Escherichia coli were purified to homogeneity by the criterion of gel electrophoresis. The first (enzyme A) is active on L-aspartic acid, L-tyrosine, L-phenylalanine, and L-tryptophan; the second (enzyme B) is active on the aromatic amiono acids. Enzyme A is identical in substrate specificity with transaminase A and is mainly an aspartate aminotransferase; enzyme B has never been described before and is an aromatic amino acid aminotransferase. The two enzymes are different in the Vmax and Km values with their common substrates and pyridoxal phosphate, in heat stability (enzyme A being heat-stable and enzyme B being heat-labile at 55 degrees) and in pH optima with the amino acid substrates. They are similar in their amino acid composition, each enzyme appears to consist of two subunits, and enzyme B may be converted to enzyme A by controlled proteolysis with subtilsin. The conversion was detected by the generation of new aspartate aminotransferase activity from enzyme B and was further verified by identification by acrylamide gel electrophoresis of the newly formed enzyme A. The two enzymes appear to be products of two genes different in a small, probably terminal, nucleotide sequence.
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PMID:Multispecific aspartate and aromatic amino acid aminotransferases in Escherichia coli. 23 11

The interactions were studied of the apoenzyme of aspartate aminotransferase from chicken heart cytosol with a variety of pyridoxal-P analogues. 2-Norpyridoxal-P, 2'-n-propylpyridoxal-P, 2'-isopropylpyridoxal-P, 6-methylpyridoxal-P, and 5'-methylpyridoxal-P were shown to display coenzyme activity. Estimated relative Vmax values of the complexes of apoenzyme with the above--mentioned analogues amounted respectively to 0.8; 0,2; 0,1; 0.1 and 0.1 (taking the Vmax value of the native holoenzyme as equal 1.0). The pH-dependence of reactivation rates of the apoenzyme with pyridoxal-P and pyridoxamine-P was evaluated. 3-Deoxypyridoxal-P, 3-0-methylpyridoxal-P, 2'-phenylpyridoxal-P, 5-nor-5-beta-carboxyvinylpyridoxal and 5-nor-5-beta-carboxyethylpyridoxal fail to activate the apoenzyme, but inhibit competitively the binding of pyridoxal-P to the protein; the estimated Ki values for these analoges were 2.4-10- minus 6; 3.1-10- minus 6; 3.5-10- minus 6; 7.2-10- minus 6 and 8.3-10- minus 6 M, respectively. It is of interest to compare reactivation effects of pyridoxal-P analogues for the apoenzymes of aspartate aminotransferases from chicken and from pig heart cytosol. Although the observed effects were fairly similar, it should be noted that the relative catalytic efficiencies of complexes of the chicken apoenzyme with pyridoxal-P analogues were much lower than those of complexes formed with the pig heart apoenzyme. It thus appears that of the two enzymes tested, the chicken heart aminotransferase makes more stringent demands with respect to structure of the coenzyme.
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PMID:[Interaction of aspartate transaminase from chicken heart cytosol with pyridoxal phosphate analogs]. 23 82


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