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Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The properties of crude and purified mitochondrial aspartate aminotransferase preparations from pyridoxine-deficient and control rat livers were compared. The preparations from the two sources showed very similar behaviors on heat treatment, electrophoresis and chromatofocusing, and had similar molecular weights, but their visible absorption spectra and circular dichroism properties were different. These results suggest that mitochondrial aspartate aminotransferase from pyridoxine-deficient and control rat livers have very similar properties, but differ somewhat in conformation in the region of the pyridoxal phosphate binding site.
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PMID:Characterization of mitochondrial aspartate aminotransferase from the liver of pyridoxine-deficient rats. 400 65

Chicken liver aspartate aminotransferase was inhibited by several inorganic anions. The inhibitory effect of the anions was related to their chaotropic character. Apparent Km (2-oxoglutarate) and Km (L-aspartate) values depended on the molarity of the buffer. The profile of the curves obtained did not depend on the nature of the enzyme sample assayed. Phosphate slightly inhibited the holoaspartate aminotransferase and was a strong inhibitor of apoaspartate aminotransferase with respect to pyridoxal phosphate.
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PMID:Effect of phosphate and other inorganic anions on the activity of chicken liver cytosolic aspartate aminotransferase. 404 12

Cytosolic chicken heart aspartate aminotransferase (EC 2.6.1.1) was incorporated in polyacrylamide gel and partially oriented by compressing the gel block in two mutually perpendicular directions. The linear dichroism (LD) was recorded in a dichrograph equipped with a quarter-wavelength device which transforms circularly polarized light into linearly polarized. Spectra were resolved with lognormal distribution curves. A marked difference has been found between reduced linear dichroism values (LD/A) in the absorption bands of the protonated (430 nm) and nonprotonated (360 nm) forms of the internal pyridoxal phosphate--lysine aldimine. This finding indicates that protonation of the internal aldimine bond induces a change in direction of the transition dipole moment within the coenzyme ring or reorientation of the ring. Formation of the external aldimine with 2-methylaspartate is accompanied by a decrease of the reduced LD value in the 430 nm band. On the other hand, binding of the dicarboxylate anions, which imitates formation of the noncovalent adsorption Michaelis complex, results in a marked increase of the reduced LD value in the 430 nm band. These data suggest that the coenzyme ring tilts in opposite directions upon noncovalent substrate binding and upon subsequent formation of the external aldimine.
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PMID:[Linear dichroism of chicken cytosol aspartate aminotransferase oriented in polyacrylamide gel]. 407 36

1. The effect of pH change on the reconstitution of aspartate aminotransferase (EC 2.6.1.1), i.e. the reactivation of the apoenzyme with coenzyme (pyridoxal phosphate and pyridoxamine phosphate), was studied in the pH range 4.2-8.9 by using three buffer systems at concentrations ranging from 0.025 to 0.1m. 2. Although the profile of the reconstitution rate-pH curve in the range pH5.2-6.8 (covered by sodium cacodylate-HCl buffer) reflects the influence of the H(+) concentration on the reconstitution process, the profile of the curve in the pH ranges 4.2-5.6 and 7.2-8.25 (covered respectively by sodium acetate-acetic acid and Tris-HCl buffers) appears to be influenced by the ionic strength of the buffer. 3. The reconstitution is also influenced by univalent inorganic ions such as halide ions and, to a lesser extent, alkali metal ions, which are known to alter the water structure.
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PMID:Effect of pH, ionic strength and univalent inorganic ions on the reconstitution of aspartate aminotransferase. 485 93

1. N-(5'-Phosphopyridoxyl)-l-glutamic acid (P-Pxy-Glu, compound I) is readily converted at pH3 into a substance (P-Pxy-Glp, compound II) characterized as N-(5'-phosphopyridoxyl)-2-oxopyrrolidine-5-carboxylic acid. 2. The u.v., i.r. and fluorescence spectra of P-Pxy-Glu and P-Pxy-Glp have been determined; from the u.v. spectra their pK values have been found and compared. 3. The apoenzyme of aspartate aminotransferase is rapidly and irreversibly inactivated by P-Pxy-Glu, but is inactivated more slowly by P-Pxy-Glp. The complex with P-Pxy-Glp is stable enough to be isolated, but it is slowly reactivated in the presence of excess of pyridoxal phosphate. 4. The u.v. spectrum of the complex of apoenzyme and P-Pxy-Glp suggests that it contains a hydrogen bond between the phenolic hydroxyl group and the pyrrolidone nitrogen; this specifies the conformation of most of the molecule of P-Pxy-Glp. This conformation is similar to that previously postulated for the enzyme-glutamate complex except for the side chain of glutamate. Hence both the affinity of P-Pxy-Glp for the apoenzyme and the fact that it is more easily removed than P-Pxy-Glu are explicable.
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PMID:N-(5'-phosphopyridoxyl)glutamic acid and N-(5'-phosphopyridoxyl)-2-oxopyrrolidine-5-carboxylic acid and their action on the apoenzyme of aspartate aminotransferase. 512 78

Dialyzed extracts of Acetobacter suboxydans ATCC 621 catalyze (14)CO(2) assimilation in the presence of phosphoenolpyruvate and a divalent cation. The formation of (14)C-oxalacetate was demonstrated and found not to be dependent upon the presence of orthophosphate or diphosphonucleotides. Oxalacetate synthesis was stimulated by orthophosphate and inhibited by aspartate. All attempts to demonstrate a reversible carboxylation mechanism have failed. (14)C-aspartate was synthesized when phosphoenolpyruvate, H(14)Co(3) (-), pyridoxal phosphate, and glutamate were added to dialyzed extracts. Chromatographic and spectrophotometric analyses and chemical degradation further demonstrate the presence of a reversible aspartate aminotransferase. The function of oxalacetate synthesis in a bacterium that reportedly lacks an operative tricarboxylic acid cycle is discussed.
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PMID:Phosphoenolpyruvate carboxylation and aspartate synthesis in Acetobacter suboxydans. 577 23

1. Acetylation of aspartate aminotransferase from pig heart inhibits completely the enzymic activity when the coenzyme is in the amino form (pyridoxamine phosphate) or when the coenzyme has been removed, but not when the coenzyme is in the aldehyde form (pyridoxal phosphate). 2. The group the acylation of which is responsible for the inhibition has been identified with the in-amino group of a lysine residue at the coenzyme-binding site. Moreover, in the pyridoxamine-enzyme the amino group of the coenzyme is also acetylated. 3. The reactivity of the coenzyme-binding lysine residue is greatly different in the pyridoxamine-enzyme and in the apoenzyme, suggesting the possibility of an interaction of its in-amino group with pyridoxamine or with other groups on the protein.
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PMID:Acylation of aspartate aminotransferase. 604 35

1. In order to assess the effects of oestrogens on the metabolism of tryptophan and vitamin B6, ovariectomized rats have been maintained on diets providing known amounts of tryptophan, nicotinamide and vitamin B6. They received oestrone sulphate, 210 micrograms/kg body-wt per d, either incorporated in the diet for 8 weeks, or by daily intraperitoneal injection for periods of 1-3 d. 2. Oestrone sulphate administration caused a slight reduction in the concentration of pyridoxal phosphate in plasma. It had no effect on the concentration of pyridoxal phosphate in liver or kidney, the urinary excretion of 4-pyridoxic acid, the activation of erythrocyte aspartate aminotransferase (L-aspartate:2-oxo-glutarate aminotransferase, EC 2. 6. 1. 1) by incubation with added pyridoxal phosphate, or the activity of pyridoxal oxidase (aldehyde:oxygen oxido-reductase, EC 1.2.3.1) in the liver. 3. Oestrone sulphate administration caused an increase in the urinary excretion of kynurenine and a reduction in the activity of liver kynureninase (L-kynurenine hydrolase, EC 3.7.1.3). It had no effect on the urinary excretion of N1-methyl nicotinamide or the concentrations of nicotinamide nucleotides in blood, liver or kidney. 4. There was a considerable excess of the apoenzyme of kynureninase in the liver. Incubation of liver homogenates with added pyridoxal phosphate led to a 4- to 5-fold increase in activity. 5. We conclude that there is no evidence of any significant effect of oestrogens on vitamin B6. It is suggested that abnormalities of tryptophan metabolism in women receiving oestrogens, which have been widely attributed to drug-induced vitamin B6 depletion, can be accounted for by inhibition of kynureninase by oestrogen metabolites.
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PMID:Effects of oestrogen administration on vitamin B6 and tryptophan metabolism in the rat. 628 3

Inactivation of the beta 2 subunit and of the alpha 2 beta 2 complex of tryptophan synthase of Escherichia coli by the arginine-specific dicarbonyl reagent phenylglyoxal results from modification of one arginyl residue per beta monomer. The substrate L-serine protects the holo beta 2 subunit and the holo alpha 2 beta 2 complex from both inactivation and arginine modification but has no effect on the inactivation or modification of the apo forms of the enzyme. This result and the finding that phenylglyoxal competes with L-serine in reactions catalyzed by both the holo beta 2 subunit and the holo alpha 2 beta 2 complex indicate that L-serine and phenylglyoxal both bind to the same essential arginyl residue in the holo beta 2 subunit. The apo beta 2 subunit is protected from phenylglyoxal inactivation much more effectively by phosphopyridoxyl-L-serine than by either pyridoxal phosphate or pyridoxine phosphate, both of which lack the L-serine moiety. The phenylglyoxal-modified apo beta 2 subunit binds pyridoxal phosphate and the alpha subunit but cannot bind L-serine or L-tryptophan. We conclude that the alpha-carboxyl group of L-serine and not the phosphate of pyridoxal phosphate binds to the essential arginyl residue in the beta 2 subunit. The specific arginyl residue in the beta 2 subunit which is protected by L-serine from modification by phenyl[2-14C]glyoxal has been identified as arginine-148 by isolating a labeled cyanogen bromide fragment (residues 135-149) and by digesting this fragment with pepsin to yield the labeled dipeptide arginine-methionine (residues 148-149). The primary sequence near arginine-148 contains three other basic residues (lysine-137, arginine-141, and arginine-150) which may facilitate anion binding and increase the reactivity of arginine-148. The conservation of the arginine residues 141, 148, and 150 in the sequences of tryptophan synthase from E. coli, Salmonella typhimurium, and yeast supports a functional role for these three residues in anion binding. The location and role of the active-site arginyl residues in the beta 2 subunit and in two other enzymes which contain pyridoxal phosphate, aspartate aminotransferase and glycogen phosphorylase, are compared.
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PMID:L-serine binds to arginine-148 of the beta 2 subunit of Escherichia coli tryptophan synthase. 641 46

Intraperitoneal administration of isoniazid (IN), an antituberculous agent, to mice or rats at a dose of 100 mg/kg body weight resulted in remarkable and rapid inhibition of liver cytosolic aspartate aminotransferase (AAT); inhibition was less marked with other antivitamin B6 compounds; AATs in other tissues and other aminotransferases in liver were less effectively inhibited by IN. The inhibition of liver cytosolic AAT was apparently irreversible in vivo; it was reversed only a little by gel filtration and dialysis to remove excess IN in vitro, although treatment with pyridoxal phosphate or 5'-deoxypyridoxal slowly restored the full activity. Attempts to inhibit the enzyme by in vitro treatments showed that IN itself was not an effective inhibitor, while the liver extracts from IN treated mice contained some strongly inhibitory substance. In addition, the extracts were shown to contain only trace amounts of IN. These results suggest that IN is metabolized to some other form which is markedly inhibitory to murine liver cytosolic AAT, and the metabolite binds to the coenzyme moiety of enzyme in a manner not readily dissociable.
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PMID:"In vivo" inhibition of murine liver aspartate aminotransferase by isoniazid. 646 31


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