Synonyms: B0928 , Aat , AspC

Comment:
The enzyme is a dimeric form composed of two identical subunits. Each subunit has two domains, a small and a large one. In each subunit there exists a PLP molecule forming a Schiff base with a lysine residue. The crystal structure has been determined [ Smith89 , Kamitori90 ] Aspartate 222 and tyrosine 70 play important roles at the active site. [ Yano92 , Shibayama91 ]

Gene: aspC

Locations: cytoplasm

Subunit composition of aspartate transaminase = [AspC]₂

Sequence Length: 396 AAs

Molecular Weight of Polypeptide (from nucleotide sequence): 43.573 kD

pI: 5.8

GO Terms:
GO:0006532 - aspartate biosynthesis ,
GO:0009063 - amino acid catabolism ,
GO:0005737 - cytoplasm

Unification Links: MODBASE:P00509 , PDB:1AAM , PDB:1AAW , PDB:1AHE , PDB:1AHF , PDB:1AHG , PDB:1AHX , PDB:1AHY , PDB:1AIA , PDB:1AIB , PDB:1AIC , PDB:1AMQ , PDB:1AMR , PDB:1AMS , PDB:1ARG , PDB:1ARH , PDB:1ARI , PDB:1ARS , PDB:1ART , PDB:1ASA , PDB:1ASB , PDB:1ASC , PDB:1ASD , PDB:1ASE , PDB:1ASF , PDB:1ASG , PDB:1ASL , PDB:1ASM , PDB:1ASN , PDB:1B4X , PDB:1BQA , PDB:1BQD , PDB:1CQ8 , PDB:1G4V , PDB:1G4X , PDB:1G7W , PDB:1G7X , PDB:1IX6 , PDB:1IX7 , PDB:1IX8 , PDB:1QIR , PDB:1QIS , PDB:1QIT , PDB:1SPA , PDB:1YOO , PDB:2AAT , PDB:3AAT , PDB:5EAA , RefSeq:NP_415448 , UniProtKB:P00509

Relationship Links: Pfam:IN-FAMILY:PF00155

Gene-Reaction Schematic:

Enzymatic reaction of: aspartate transaminase

Synonyms: aspartate aminotransferase , transaminase A (sic) , glutamic-oxoaloacetic transaminase , glutamic-aspartic transaminase , tyrosine non-repressible aspartate aminotransferase , AspAT

L-aspartate + α-ketoglutarate <=> oxaloacetate + L-glutamate

The reaction direction shown, that is, A + B <==> C + D versus C + D <==> A + B, is in accordance with the Enzyme Commission system.

This reaction is reversible.

Alternative Substrates for L-aspartate: L-tyrosine , L-phenylalanine

In Pathways: glutamate degradation II , aspartate biosynthesis I

Comment:
The aspC-gene product, the aspartate aminotransferase, is active in the synthesis in vivo of aspartate, tyrosine, and phenylalanine. [ Fotheringh86 ] The reaction is catalyzed via a ping-pong Bi-Bi mechanism in which the cofactor converts between the pyridoxal phosphate and pyridoxamine phosphate form. [ Danishefsk91 ] When an amino acid subsrate binds to to the PLP form of AspAT, a new aldimine bond is formed between the subsrate and PLP. The next step is the withdrawal of the 2-hydrogen atom of the substrate. The deprotonation leads to the formation of a quinonoid intermediate, which should represent one transition-state structure. The next reaction is the addition of a proton to the coenzyme, leading to the formation of the ketimine intermediate. The ketimine intermediate is then hydrolyzed to form a keto acid substrate and the PMP form of the enzyme. [ Kuramitsu90 ] Kinetic studies have been made [ Yano91 , Inoue91 , Kuramitsu90 ] Aspartate aminotransferase is capable of utilizing the aromatic amino acids as substrates. The enzyme exhibits broad substrate specificity. Direct transamination occurs between oxaloacetate and phenylalanine. [ Powell78 , Kuramitsu85 ] The enzyme has been crystallized. [ Kamitori90 , Smith89 ]

Citations: [ Kondo87 , Kamitori90 , Inoue91 , Danishefsk91 , Powell78 , Collier72 , Gelfand77 , Yano91 , Yano92 ]

Prosthetic Groups: pyridoxal 5'-phosphate

Cofactor Binding Comment: Aminotransferases almost without exception require pyridoxal 5'phosphate as a cofactor, which is covalently bound to the enzyme by the formation of a Schiff base with the E-amino group of a lysine residue [ Fotheringh86 ]

Inhibitors (Unknown Mechanism): 2-methylaspartate , maleate [ Danishefsk91 ]

References

Collier72: Collier RH, Kohlhaw G (1972). "Nonidentity of the aspartate and the aromatic aminotransferase components of transaminase A in Escherichia coli." J Bacteriol 1972;112(1);365-71. PMID: 4404056

Danishefsk91: Danishefsky AT, Onnufer JJ, Petsko GA, Ringe D (1991). "Activity and structure of the active-site mutants R386Y and R386F of Escherichia coli aspartate aminotransferase." Biochemistry 1991;30(7);1980-5. PMID: 1993208

Fotheringh86: Fotheringham IG, Dacey SA, Taylor PP, Smith TJ, Hunter MG, Finlay ME, Primrose SB, Parker DM, Edwards RM (1986). "The cloning and sequence analysis of the aspC and tyrB genes from Escherichia coli K12. Comparison of the primary structures of the aspartate aminotransferase and aromatic aminotransferase of E. coli with those of the pig aspartate aminotransferase isoenzymes." Biochem J 1986;234(3);593-604. PMID: 3521591

Gelfand77: Gelfand DH, Steinberg RA (1977). "Escherichia coli mutants deficient in the aspartate and aromatic amino acid aminotransferases." J Bacteriol 1977;130(1);429-40. PMID: 15983

Inoue91: Inoue K, Kuramitsu S, Okamoto A, Hirotsu K, Higuchi T, Kagamiyama H (1991). "Site-directed mutagenesis of Escherichia coli aspartate aminotransferase: role of Tyr70 in the catalytic processes." Biochemistry 1991;30(31);7796-801. PMID: 1868057

Kamitori90: Kamitori S, Okamoto A, Hirotsu K, Higuchi T, Kuramitsu S, Kagamiyama H, Matsuura Y, Katsube Y (1990). "Three-dimensional structures of aspartate aminotransferase from Escherichia coli and its mutant enzyme at 2.5 A resolution." J Biochem (Tokyo) 1990;108(2);175-84. PMID: 2121725

Kondo87: Kondo K, Wakabayashi S, Kagamiyama H (1987). "Structural studies on aspartate aminotransferase from Escherichia coli. Covalent structure." J Biol Chem 1987;262(18);8648-57. PMID: 3298240

Kuramitsu85: Kuramitsu S, Inoue K, Ogawa T, Ogawa H, Kagamiyama H (1985). "Aromatic amino acid aminotransferase of Escherichia coli: nucleotide sequence of the tyrB gene." Biochem Biophys Res Commun 1985;133(1);134-9. PMID: 3907634

Kuramitsu90: Kuramitsu S, Hiromi K, Hayashi H, Morino Y, Kagamiyama H (1990). "Pre-steady-state kinetics of Escherichia coli aspartate aminotransferase catalyzed reactions and thermodynamic aspects of its substrate specificity." Biochemistry 1990;29(23);5469-76. PMID: 2201406

Powell78: Powell JT, Morrison JF (1978). "The purification and properties of the aspartate aminotransferase and aromatic-amino-acid aminotransferase from Escherichia coli." Eur J Biochem 1978;87(2);391-400. PMID: 352693

Shibayama91: Shibayama N, Imai K, Hirata H, Hiraiwa H, Morimoto H, Saigo S (1991). "Oxygen equilibrium properties of highly purified human adult hemoglobin cross-linked between 82 beta 1 and 82 beta 2 lysyl residues by bis(3,5-dibromosalicyl) fumarate." Biochemistry 1991;30(33);8158-65. PMID: 1907852

Smith89: Smith DL, Almo SC, Toney MD, Ringe D (1989). "2.8-A-resolution crystal structure of an active-site mutant of aspartate aminotransferase from Escherichia coli." Biochemistry 1989;28(20);8161-7. PMID: 2513875

Yano91: Yano T, Kuramitsu S, Tanase S, Morino Y, Hiromi K, Kagamiyama H (1991). "The role of His143 in the catalytic mechanism of Escherichia coli aspartate aminotransferase." J Biol Chem 1991;266(10);6079-85. PMID: 2007566

Yano92: Yano T, Kuramitsu S, Tanase S, Morino Y, Kagamiyama H (1992). "Role of Asp222 in the catalytic mechanism of Escherichia coli aspartate aminotransferase: the amino acid residue which enhances the function of the enzyme-bound coenzyme pyridoxal 5'-phosphate." Biochemistry 1992;31(25);5878-87. PMID: 1610831