Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.6.1.1 (aspartate aminotransferase)
 21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hydroxyl groups of poly(ethyleneglycol) have been esterified (partly) with a number of carboxylic acids. When these esters are included in dextranpoly(ethyleneglycol)-water biphasic systems the partitions of proteins and membranes between the two phases (and the interface) are in some cases strongly affected. The affinity of serum albumin for the poly(ethyleneglycol)-rich phase is strongly increased when the fatty acid group consists of more than 10 carbon atoms. The partition also depends on the number of double bonds in the fatty acid. A corresponding relationship is found for membranes from spinach chloroplasts. The partitions of ovalbumin, lysozyme (EC 3.2.1.17) and ribonuclease (EC 3.1.4.22) are not influenced by the fatty acid esters. Esters of dibasic carboxylic acids show a minute but marked effect on the partition of proteins in general while malate and tartrate esters affect strongly the partition of chloroplast membranes. The partitions of both proteins and membranes are influenced by poly(ethyleneglycol) deoxycholate. Experiments with malate dehydrogenase (EC 1.1.1.37), lactate dehydrogenase (EC 1.1.1.27), fumarase (EC 4.2.1.2), enolase (EC 4.2.1.11) and glutamate-ocaloacetate transaminase (EC 2.6.1.1) show that their partitions, measured on enzymic activity basis, is changed when esters of benzoic, linolenic, tartaric or deoxycholic acid are included in the biphasic system. The mechanism behind the effect of the esterified poly (ethyleneglycol) on the partition of biomaterial, in this type of aqueous biphasic systems, is discussed in terms of a direct binding of the esters to the partitioned material.
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PMID:The effect of poly(ethyleneglycol) esters on the partition of proteins and fragmented membranes in aqueous biphasic systems. 99 68

The activity of enzymes of glycine and alanine synthesis (glutamate-pyruvate aminotransferase, aspartate-beta-decarboxylase, threonine aldolase, serine hydroxymethyltransferase, alanine-glyoxylate aminotransferase, aspartate aminotransferase) is studied in haemolymph, fat body, fibroin and sericine divisions of silk gland of silkworm Bombyx mori at terminal period of larva development. Alanine-glyoxylate aminotransferase activity in fibroin division of silk gland (34,6 mu mole of glycine/mg of protein/min-10(-3)), alanine aminotransferase--in sericine division (36,0 mu mole of alanine/mg of protein/min-10(-3)) aspartate aminotransferase 27,3 mu mole of glutamic acid/mg of protein/min-10(-3)) and alanine aminotransferase (35,8 mu mole of alanine/mg of protein/min-10(-3)) on fat body. The ratio of alanine-glyoxylate aminotransferase/glutamate-pyruvate aminotransferase activities in posterior division of silk gland is near to glycine/alanine ratio in silk fibroin. The character of the enzymes activity in silkworm tissues correlates with the silk formation rate.
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PMID:[Glycine and alanine synthesis enzymes in the tissues of the silkworm during its development]. 99 78

Mitochondrial and cytoplasmic isozymes of aspartate transaminase are separated from beef kidney homogenates by ammonium sulfate fractionation. The mitochondrial isozyme is purified essentially as described earlier (Eur. J. Biochem., 1972, 26, 196-206) with slight modification in order to increase the yield. The cytoplasmic isozyme is purified by heat treatment followed by ion exchange cellulose chromatography and gel chromatography. The enzyme is pure in the ultracentrifuge and in polyacrylamide gel electrophoresis; it shows only one anionic band and no subforms. It has a molecular weight of 93,000 +/- 2000 and is composed of two subunits of 46,000 M.W. The enzyme has a specific activity of 49 micronmoles of oxalacetate x min-1 x mg-1. It contains 5 SH groups per subunit; three are directly titratable with p-mercuribenzoate and the other two only after addition of 0.2% SDS; there is no evidence of S-S groups. Km values for aspartate, glutamate, alpha-ketoglutarate and oxalacetate are in the order 1.25, 3.2, 0.06 and 0.41 mM in the cytoplasmic isozyme and 0.7, 5.0, 1.25 and 0.12 mM in the mitochondrial one.
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PMID:Simultaneous purification of mitochondrial and cytoplasmic isozymes of aspartate aminotransferase from beef kidney. 103 66

Mitochondrial aspartate aminotransferase from beef kidney is 50% inhibited after 2 hr treatment with 2.5 mM tetranitromethane at pH 8. Two tyrosine residues per enzyme protomer (46,000 daltons) are modified by the reagent either in the holoenzyme or in the apoenzyme. In both cases the five SH groups titratable with p-mercuribenzoate are not modified by the reagent. However, with a tetranitromethane concentration higher than 2.5 mM and 10 mM mercaptoethanol, an additional tyrosine residue is nitrated in both holo- and apoenzymes. These results are not affected by the presence in the incubation mixture of the substrates alpha-ketoglutarate and glutamate both at ten times their Km values. Mercaptoethanol does not impair the recombination of native or nitrated apoenzyme with the coenzyme and does not reduce the coenzyme moiety of native or nitrated holoenzyme, but promotes a conformational change in the nitrated holoenzyme which causes inactivation. Hydrosulfite promotes the reduction of the coenzyme moiety of native and nitro holoenzyme resulting in their inactivation, largely in the nitrated form. The recombination of the coenzyme with native or nitrated apoenzyme is not influenced by hydrosulfite.
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PMID:Role of tyrosine residues in mitochondrial aspartate aminotransferase from beef kidney. 117 45

Glutamate aspartate transaminase (EC 2.6.1.1) is a dimeric enzyme with identical subunits with each active site containing pyridoxal 5'-phosphate linked via an internal Shiff's base to a lysine residue. It is not known if these sites interact during catalysis but negative cooperativity has been reported for binding of the coenzyme (Arrio-Dupont, M. (1972), Eur. J. Biochem. 30, 307). Also nonequivalence of its subunits in binding 8-anilinonaphthalene-1-sulfonate (Harris, H.E., and Bayley, P. M. (1975), Biochem. J. 145, 125), in modification of only a single tyrosine with full loss of activity (Christen, P., and Riordan, J.F. (1970), Biochemistry 9, 3025), and following modification with 5,5'-dithiobis(2-nitrobenzoic acid) (Cournil, I., and Arrio-Dupont, M. (1973), Biochemie 55, 103) has been reported. However, steady-state and transient kinetic methods as well as direct titration of the active site chromophore with substrates and substrate analogs have not revealed any cooperative phenomena (Braunstein, A. E. (1973), Enzymes, 3rd Ed. 9, 379). It was therefore decided that a more direct approach should be used to clarify the quistion of subunit interaction during the covalent phase of catalysis. To this end a hybrid method was devised in which a hybrid transaminase was prepared which contained one subunit with a functional active site while the other subunit has the internal Shiff's base reduced with NaBH4. The specific activities and amount of "actively bound" pyridoxal 5'-phosphate are both in a 2:1 ratio for the native and hybrid forms. Comparison of the steady-state kinetic properties of the hybrid and native enzyme forms shows that both forms gave parallel double reciprocal plots which is characteristic of the Ping-Pong Bi-Bi mechanism of transamination. The Km values for the substrates L-aspartic acid and alpha-ketoglutaric acid are nearly identical while the Vmax value for the hybrid is one-half the value of the native transaminase. It therefore appears that the active sites of glutamate aspartate transaminase function independently and a compulsory flip-flop mechanism is not involved.
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PMID:Hybridization of glutamate aspartate transaminase. Investigation of subunit interaction. 117 14

Frontal and zonal analysis of the chromatography of aspartate aminotransferase (EC2.61.1), pig heart cytosolic enzyme, on Bio-Gel P150 shows that holo- and apoenzyme can dissociate at pH 8.3. Ultracentrifugation and fluorescence depolarization confirm this result. Kinetic analysis of the fluorescence depolarization experiments favors a biphasic phenomenon: a few minutes for the faster one and several hours for the slower one. The apparent dissociation constant is 0.8 muM for the apoenzyme and 0.18 muM for the pyridoxal 5'-phosphate form of the holoenzyme. In the presence of sucrose or 0.1 M L-aspartate or a mixture of 70 mM L-glutamate and 2 mM alpha-ketoglutarate, the holoenzyme is dimeric at concentrations higher than 5 nM. The addition of a mixture of the substrates L-glutamate and alpha-ketoglutarate to a monomeric holoenzyme leads to dimerization. The stability of the dimeric form is in the order: holoenzyme + substrates greater than apoenzyme.
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PMID:Dissociation of aspartate aminotransferase into subunits. Effect of ligands upon this dissociation. 119 65

Octanoate and L-palmitylcarnitine inhibited the synthesis of P-enolpyruvate from alpha-ketoglutarate and malate by isolated guinea pig liver mitochondria. A 50% reduction in P-enolpyruvate formation was obtained with 0.1 to 0.2 mM octanoate or with 0.06 to 0.10 mM L-palmitylcarnitine. At these concentrations, oxidative phosphorylation remained intact and only much higher concentrations of fatty acids altered this process. The addition of NH4Cl in the presence of malate and increasing concentrations of alpha-ketoglutarate (or vice versa) enhanced the formation of glutamate, aspartate, and P-enolpyruvate. The addition of increasing concentrations of NH4Cl in the presence of fixed amounts of malate and alpha-ketoglutarate had a similar effect. Furthermore, the inhibition of P-enolpyruvate synthesis by fatty acids and the reduction of the acetoacetate to beta-hydroxybutyrate ratio were reversed by the addition of NH4Cl. Cycloheximide, which blocks energy transfer at site 1 of the respiratory chain, decreased P-enolpyruvate formation. When cycloheximide and either octanoate or L-palmitylcarnitine were added together, there was an even greater reduction in P-enolpyruvate synthesis from either malate or alpha-ketoglutarate than was noted with either fatty acid alone. Since cycloheximide lowers the rate of ATP synthesis this may in turn reduce P-enolpyruvate formation by a mechanism independent of changes in the mitochondrial NAD+/NADH ratio caused by fatty acids. In the isolated perfused liver metabolizing lactate, the inhibitory effect of octanoate on gluconeogenesis was partially relieved by the addition of 1 mM NH4Cl, but remained unchanged in the presence of 2 mM NH4Cl, despite a highly oxidized NAD+/NADH ratio in the mitochondria. In contrast to glucose synthesis, urea formation was markedly increased during the infusion of 1 mM as well as 2 mM NH4Cl. After cessation of NH4Cl infusion, there was an increase in glucose production, to a rate as high as that observed in the absence of octanoate. This increase was accompanied by the disappearance of alanine, aspartate, and glutamate which had been stored in the liver during NH4Cl infusion. Urea synthesis also decreased progressively. These results indicate that gluconeogenesis in guinea pig liver is regulated, in part, by alterations in the mitochondrial oxidation-reduction state. However, the modulation of this effect by changing the concentrations of intermediates of the aspartate aminotransferase reaction indicates competition for oxalacetate between the aminotransferase reaction and P-enolpyruvate carboxykinase.
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PMID:Regulation of hepatic gluconeogenesis in the guinea pig by fatty acids and ammonia. 119 71

1. Isolated hepatocytes were used to establish the reasons for the accumulation of aspartate, previously observed when the isolated rat liver was perfused with ethanol in the presence of alanine or ammonium lactate. 2. The isolated cells did not form aspartate when incubated with alanine and ethanol, but much aspartate was formed on incubation with ammonium lactate and ethanol. 3. Urea was the main nitrogenous product on incubation with alanine, in contrast with the perfused liver, where major quantities of NH4+ are also formed. When the formation of urea was nullified by the addition of urease, alanine plus ethanol caused aspartate formation, indicating that aspartate formation depends on the presence of critical concentrations of NH4+. 4. The accumulated aspartate was present in the cytosol. Ethanol halved the content of 2-oxoglutarate in the cytosol and more than trebled that of glutamate in the mitochondria. 5. The findings support the assumption that 2-oxoglutarate formed by the mitochondrial aspartate aminotransferase is not translocated to the cytosol in the presence of ethanol and NH4+, because it is rapidly converted into glutamate, the dehydrogenation of ethanol providing the required NADH. Aspartate, however, is translocated to the cytosol and accumulates there because of the lack of stoicheiometric amounts of oxoglutarate.
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PMID:The accumulation of aspartate in the presence of ethanol in rat liver. 120 Oct 7

The hydrogen exchange at the Beta-carbon of L-alanine, L-glutamate and L-asparate with water has been examined during transamination catalyzed by glutamic-oxaloacetic transaminase and by glutamic-pyruvic transaminase. A significant hydrogen exchange at the Beta-carbon has been demonstrated during incubation of L-[3-3H]alanine + glutamic-pyruvic transaminase, L-[3-3H]alanine + alpha-oxo-glutarate + glutamic-pyruvic transaminase, L-[3-3H]glutamate + glutamic-oxaloacetic transaminase, L-[3-3H]glutamate + oxaloacetate +glutamic-oxaloacetic transaminase, and L-[3-3H]glutamate + pyruvate + glutamic-pyruvic transaminase as shown by the appearance of 3H2O. No hydrogen exchange at the Beta-carbon of L-glutamate occurred during incubation of L-[3-3H]-glutamate with glutamic-pyruvic transaminase alone. The hydrogen exchaned at the Beta-carbon of L-glutamate coincides with transamination as demonstrated by nuclear magnetic resonance studies of 2H2O-L-glutamate exchange during transamination by glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase. No hydrogen exchange at the Beta-carbon occurred during transamination of L-aspartate by glutamic-oxaloacetic transaminase as shown by nuclear magnetic resonance spectroscopy and confirmed by nuclear magnetic resonance simulation studies. The results are discussed with special reference to the different equilibria between the pyridoxal form and the pyridoxamine form of glutamic-oxaloacetic transaminase and of glutamic-pyruvic transaminase.
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PMID:Hydrogen exchane at the beta-carbon of amino acids during transamination. 120 22

Chinese hamster ovary cells with a specific auxotrophy for proline were fused with human cells from a variety of sources and the resulting hybrids analyzed for human genetic markers. Of 63 hybrid clones examined, 27 possessed both proline and cytoplasmic glutamate oxaloacetate transaminase markers; 36 had neither; and no clones were found possessing one and not the other. These results constitute evidence that the proline and glutamate oxalocetate transaminase markers are syntenic. Evidence for absence of synteny between these and a variety of other human genes is presented. Biochemical tracer experiments established that the proline biosynthetic pathway through glutamate has been restored in the Pro+ hybrids.
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PMID:Synteny between the pro+ marker and human glutamate oxaloacetate transaminase. 123 10


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