Aspartate aminotransferase transamination

Pyridoxamine phosphate serves as a coenzyme of transaminases, e.g., lysyl oxidase (collagen biosynthesis), serine hydroxymethyl transferase (Cl-metabolism), S-aminolevulinate synthase (porphyrin biosynthesis), glycogen phosphoiylase (mobilization of glycogen), aspartate aminotransferase (transamination), alanine aminotransferase (transamination), kynureninase (biosynthesis of niacin), glutamate decarboxylase (biosynthesis of GABA), tyrosine decarboxylase (biosynthesis of tyramine), serine dehydratase ((3-elimination), cystathionine 3-synthase (metabolism of methionine), and cystathionine y-lyase (y-elimination). 

Unnatural Amino Acids by Enzymatic Transamination Synthesis of Glutamic Acid Analogues with Aspartate Aminotransferase... 

Figure 8.11 Five near-equilibrium reactions involved in transamination of five different amino adds. Three enzymes are involved in these reactions (1) alanine aminotransferase (2) aspartate aminotransferase (3) branched-chain amino acid aminotransferase, i.e. one enzyme catalyses the three reactions. (The branched-chain amino acids are essential.)...

The oxaloacetate is then transported from mitochondrion into the cytosol but not directly, since there is no transporter for oxaloacetate in the mitochondrial membrane. This problem is solved by conversion of oxaloacetate to aspartate, by transamination, and it is the aspartate that is transported across the inner mitochondrial membrane to the cytosol, where oxaloacetate is regenerated from aspartate by a cytosolic aminotransferase enzyme. 

In the malate shuttle (left)—which operates in the heart, liver, and kidneys, for example-oxaloacetic acid is reduced to malate by malate dehydrogenase (MDH, [2a]) with the help of NADH+HT In antiport for 2-oxogluta-rate, malate is transferred to the matrix, where the mitochondrial isoenzyme for MDH [2b] regenerates oxaloacetic acid and NADH+HT The latter is reoxidized by complex I of the respiratory chain, while oxaloacetic acid, for which a transporter is not available in the inner membrane, is first transaminated to aspartate by aspartate aminotransferase (AST, [3a]). Aspartate leaves the matrix again, and in the cytoplasm once again supplies oxalo-acetate for step [2a] and glutamate for return transport into the matrix [3b]. On balance, only NADH+H"" is moved from the cytoplasm into the matrix ATP is not needed for this. 

Figure 9-1. Molecular interconversions in handling of ammonia. The major enzyme responsible for interconversion of glutamate and a-ketoglutarate is glutamate dehydrogenase. No free ammonia is ever present during direct transfer of amino groups from alanine or aspartate via transamination to produce glutamate. ALT, alanine aminotransferase AST, aspartate aminotransferase.

Transamination and the Urea Cycle Aspartate aminotransferase has the highest activity of all the mammalian liver aminotransferases. Why ... 

In the other, the amino acid is rotated 180° so that the a-hydrogen protrudes behind the plane of the paper. Dunathan studied pyridoxamine pyruvate aminotransferase, an enzyme closely related to PLP-requiring aminotransferases and which catalyzes the transamination of pyridoxal with L-alanine to form pyridox-amine and pyruvate. The same reaction is catalyzed by the apoenzyme of aspartate aminotransferase. In both cases, when the alanine contained 2H in the a position the 2H was transferred stereospecifically into... 

Absorption bands at 500 nm. With many PLP enzymes certain substrates and inhibitors cause the appearance of intense and unusually narrow bands at 500 nm. Such a band is observed with aspartate aminotransferases acting on eryf/zro-3-hydroxyaspartate (Fig. 14-9). This substrate undergoes transamination very slowly, and the 500-nm absorbing form which accumulates is probably an intermediate in the normal reaction sequence. A similar spectrum is produced by tryptophan indole-lyase acting on the competitive inhibitor L-alanine. Under the same conditions the... 

Figure 14-10 Models of catalytic intermediates for aspartate aminotransferase in a half-transamination reaction from aspartate to oxalocetate. For clarity, only a selection of the active site groups are shown. (A) Michaelis complex of PLP enzyme with aspartate. (B) Geminal diamine. (C) Ketimine intermediate. The circle indicates a bound water molecule. See Jansonius and Vincent in Jurnak and McPherson.163 Courtesy of J.N. Jansonius.

Aspartate aminotransferase 57s, 135s, 753 absorption spectra 749 active site structure 744 atomic structure 750 catalytic intermediates, models 752 NMR spectra 149 quinonoid intermediate 750 Ramachandran plot 61 sequence 57 transamination 742 Aspartate ammonia-lyase 685 Aspartate carbamoyltransferase 348s active sites 348 regulation 540... 

Aspartate aminotransferase (AAT) transamination decarboxylation in wt, transamination dominates Yano, 1998 Oue, 1999... 

Answer The second amino group introduced into urea is transferred from aspartate. This amino acid is generated in large quantities by transamination between oxaloacetate and glutamate (and many other amino acids), catalyzed by aspartate aminotransferase. Approximately one half of all the amino groups excreted as urea must pass through the aspartate aminotransferase reaction, and liver contains higher levels of this aminotransferase than of any other. 

Oxoglutarate is the normal acceptor of the amino group. In the aminotransferase reaction, 2-oxoglutarate is transaminated to give glutamate. There are at least 13 different aminotransferases, but their specificities are not all known. The most important are (a) aspartate aminotransferase, which catalyzes the following reversible reaction ... 

Steps in the Transaminase Reaction Purified aspartate aminotransferase is capable of catalyzing the half-reaction of transamination (very slowly) in the crystal. This means that the conformational changes that occur during the reaction can be followed by X-ray diffraction crystallography. 

The answer is e. (Murray, pp 505-626. Scriver, pp 4029-4240. Sack, pp 121-138. Wilson, pp 287-320.) Aspartate is a glucogenic amino acid that is also used to carry NH/ into the urea cycle. Aspartate aminotransferase catalyzes the direct transamination of aspartate to oxaloacetate ... 

L-Phosphinothricin, the active ingredient of the broad-spectrum herbicide Basta (AgrEvo), can be obtained through enzymatic transamination of the corresponding oxoacid, 2-oxo-4-[(hydroxy)(methyl)phosphinoyl]butyric acid, in a coupled system with aspartate aminotransferase (AAT) and 4-aminobutyrate 2-ketoglutarate transaminase (E.C. 2.6.1.19) from E. coli (Fig. 12.7-6)[37 . In solutions containing 10% substrate, 85 % conversion was reached with only < 3 % amino acid by-products. For... 

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