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37-454: Branched-chain amino acid aminotransferase ( BCAT ), also known as branched-chain amino acid transaminase , is an aminotransferase enzyme ( EC 2.6.1.42 ) which acts upon branched-chain amino acids (BCAAs). It is encoded by the BCAT2 gene in humans. The BCAT enzyme catalyzes the conversion of BCAAs and α-ketoglutarate into branched chain α-keto acids and glutamate . The structure to

74-476: A beta-pleated sheet . Structural studies of human branched-chain amino acid aminotransferases (hBCAT) revealed that the peptide bonds in both isoforms are all trans except for the bond between residues Gly338-Pro339. The active site of the enzyme lies in the interface between the two domains. Like other transaminase enzymes (as well as many enzymes of other classes), BCATs require the cofactor pyridoxal-5'-phosphate (PLP) for activity. PLP has been found to change

111-464: A few adult tissues, they are expressed at a high level during embryogenesis. The cytosolic isoform has a higher turnover rate, approximately 2-5 times faster than the mitochondrial isoform. BCATc has been found to be more stable than BCATm, with evidence suggesting 2 sulfide bonds. The cytosolic isozyme demonstrates no loss in activity upon titration of one thiol group hBCATc demonstrates a lower redox potential (approximately 30 mV) than hBCATm. Human BCATc

148-475: A loss in BCKD-stimulated insulin secretion, but has not been associated with losses in insulin secretion from other metabolic pathways. BCATc regulates the mTORC1 signaling and TCR-induced glycolytic metabolism pathways during CD4 T cell activation. In the brain, BCATc regulates the amount of glutamate production for use as a neurotransmitter or for future γ-Aminobutyric acid (GABA) synthesis. BCATs also play

185-413: A medium lacking the right amino acid ratios for growth must be able to synthesize branched chain amino acids in order to proliferate. In Streptococcus mutans , the gram-positive bacteria that lives in human oral cavities and is responsible for tooth decay, amino acid biosynthesis/degradation has been found to regulate glycolysis and maintain the internal pH of the cell. This allows the bacteria to survive in

222-513: A molecular weight of 38 kDa. Because branched chain amino acids are crucial in the formation and function of many proteins, BCATs have many responsibilities in mammalian physiology. BCATs have been found to interact with protein disulfide isomerases, a class of enzymes that regulate cellular repair and proper protein folding. The second step of branched chain amino acid metabolism (oxidative carboxylation by branched chain ketoacid dehydrogenase) stimulates insulin secretion. Loss of BCATm correlates with

259-472: A reversible transamination followed by the oxidative decarboxylation of the transamination products α-ketoisocaproate, α-keto-β-methylvalerate, and α-ketoisovalerate to isovaleryl-CoA, 3-methylbutyryl-CoA, and isobutyryl-CoA, respectively. This reaction regulates metabolism of amino acids and is a crucial step in nitrogen shuttling throughout the whole body. Branched-chain amino acids (BCAA) are ubiquitous in many organisms, comprising 35% of all proteins and 40% of

296-627: A role in the physiology of plant species, but it has not been studied as extensively as mammalian BCATs. In Cucumis melo (melon), BCATs have been found to play a role in developing aroma volatile compounds that give melons their distinct scent and flavor. In Solanum lycopersicum (tomatoes), BCATs play a role in synthesizing the branched-chain amino acids that act as electron donors in the electron transport chain. Overall, plant BCATs have catabolic and anabolic regulatory functions. In bacterial physiology, BCATs perform both reactions, forming both α-ketoacids and branched chain amino acids. Bacteria growing on

333-478: Is a protein that in humans is encoded by the BCAT1 gene . It is the first enzyme in the branched-chain amino acid (BCAA) degradation pathway and facilitates the reversible transamination of BCAAs and glutamate. BCAT1 resides in the cytoplasm , while its isoform, BCAT2 , is found in the mitochondria . This gene encodes the cytosolic form of the enzyme branched-chain amino acid transaminase. This enzyme catalyzes

370-517: Is a drug often used to treat patients with neuropathic pain. This neuropathic pain can be caused by a number of things, including diabetic neuropathy and postherpetic neuralgia. Gabapentin is an amino acid drug structurally similar to the two neurotransmitters glutamate (synthesized by BCATs) and GABA. The drug competitively inhibits both BCAT isoforms in the brain, slowing down glutamate production. Gabapentin also inhibits GABA aminotransferase (GABA-T) and glutamate dehydrogenase (GDH), two other enzymes in

407-494: Is also a gene encoding a mitochondrial form of this enzyme (BCAT2), mutations in either gene may contribute to these disorders. Overexpression of BCAT1 has been associated with a variety of cancers , among them glioblastoma , breast cancer , acute myeloid leukemia , gastric cancer and chronic myeloid leukemia . This article incorporates text from the United States National Library of Medicine , which

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444-442: Is converted into pyridoxamine in the first half-reaction, when an amino acid is converted into a keto acid. Enzyme-bound pyridoxamine in turn reacts with pyruvate , oxaloacetate , or alpha-ketoglutarate , giving alanine , aspartic acid , or glutamic acid , respectively. Many transamination reactions occur in tissues, catalysed by transaminases specific for a particular amino/keto acid pair. The reactions are readily reversible,

481-440: Is encoded by BCAT1 Mitochondrial branched-chain amino acid aminotransferases are the more ubiquitous of the two isoforms, present in all tissues in the mitochondria of the cell. Pancreatic acinar tissue has been found to carry the highest levels of BCATm in the body In addition, two homologs to normal BCATm have been found. One homolog is found in placental tissue, and the other co-represses thyroid hormone nuclear receptors. BCATm

518-724: Is more sensitive to the redox environment of the cell, and can be inhibited by nickel ions even if the environment is reducing. BCATm has been found to form no disulfide bonds, and titration of two -SH groups with 5,5'- dithiobis(2-nitrobenzoic acid) eliminates enzyme activity completely in the case of the BCATm isozyme. In humans, BCATm is encoded by the BCAT2 gene. Plant BCATs have also been identified, but vary between species in terms of number and sequence. In studies of Arabidopsis thaliana (thale cress), six BCAT isoforms have been identified that share between 47.5-84.1% homology with each other. These isoforms also share around 30% sequence homology to

555-512: Is typically engineered to be overexpressed and extracted from whole cells to be used for chemical synthesis. Aminotransferases are used because they can accomplish a typically multi-step reaction in one step, can perform reactions on a wide range of substrates, and have high regioselectivity and enantioselectivity. In synthetic organic chemistry, BCATs are typically used for the conversion of L-Leucine to 2-ketoglutarate. The anticonvulsant gabapentin [Neurontin; 1-(aminomethyl)cyclohexaneacetic acid]

592-423: The branched chain amino acids leucine , isoleucine , and valine . In humans, branched chain amino acids are essential and are degraded by BCATs. In humans, BCATs are homodimers composed of two domains, a small subunit (residues 1-170) and a large subunit (residues 182-365). These subunits are connected by a short, looping connecting region (residues 171-181). Both subunits consist of four alpha-helices and

629-409: The branched-chain keto acid dehydrogenase complex from which the carbon backbones of each BCAA may enter distinct degradation pathways. The oncogenic transcription factor Myc is frequently reported to drive BCAT1 expression. Two different clinical disorders have been attributed to a defect of branched-chain amino acid transamination: hypervalinemia and hyperleucine-isoleucinemia. As there

666-457: The BCAT enzyme. However, the structure of the enzyme is different between organisms. In Escherichia coli , the enzyme is a hexamer containing six identical subunits. Each subunit has a molecular weight of 34 kDa and is composed of 308 amino acids. In contrast, Lactococcus lactis BCAT is a homodimer similar to the mammalian isoforms. Each subunit of the L. lactis BCAT is composed of 340 amino acids for

703-446: The CXXC motif is crucial to optimal protein folding and function. The sensitivity of both isoenzymes to oxidation make them potential biomarkers for the redox environment within the cell. Although the CXXC motif is present only in mammalian BCATs, the surrounding amino acid residues were found to be highly conserved in both prokaryotic and eukaryotic cells. Conway, Yeenawar et al. found that

740-655: The Tyr 207 and Glu237 residues. In addition, the phosphate oxygen atoms on the PLP molecule interact with the Arg99, Val269, Val270, and Thr310 residues. Mammalian BCATs show a unique structural CXXC motif (Cys315 and Cys318) sensitive to oxidizing agents and modulated through S-nitrosation, a post-translational modification that regulates cell signaling. Modification of these two cysteine residues via oxidation (in vivo/vitro) or titration (in vitro) has been found to inhibit enzyme activity, indicating that

777-437: The acidic conditions of the human oral cavity from the breakdown of carbohydrates. BCATs have been used in the synthesis of some pharmaceutical drugs as an alternative to heavy metal catalysts, which can be expensive/environmentally unfriendly. Aminotransferases (transaminases) in general have been used to create unnatural amino acids, important building blocks for peptidomimetic drugs and agricultural products. BCAT from E. coli

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814-432: The amino acids required in all mammals. Mammalian BCATs come in two isoforms: cytosolic (BCATc) and mitochondrial (BCATm). The isoforms share 58% homology, but vary in location and catalytic efficiency. Cytosolic branched-chain amino acid aminotransferases are the less common of the two isoforms, found in the cytoplasm of mammalian cells almost exclusively throughout the nervous system. Although BCATc are expressed only in

851-459: The amount of compound present. Along with the aromatic aminotransferases (AraT), BCATs in L. lactis help develop the aroma/flavor resulting from volatile sulphur compounds produced during fermentation. The bacteria Staphylococcus carnosus and Enterococcus faecalis are often used in tandem with other lactic acid bacterium to begin the meat fermentation process. BCATs in these two bacteria perform transaminations during meat fermentation, producing

888-476: The conformation of aminotransferase enzymes, locking the conformation of the enzyme via a Schiff base (imine) linkage in a reaction between a lysine residue of the enzyme and the carbonyl group of the cofactor. This conformational change allows the substrates to bind to the active site pocket of the enzymes. In addition to the Schiff base linkage, PLP is anchored to the active site of the enzyme via hydrogen bonding at

925-507: The corresponding α-ketoacids from amino acids. As fermentation proceeds, these α-ketoacids degrade into a class of compounds known as methyl-branched volatiles that include aldehydes, alcohols, and carboxylic acids, all of which contribute to the distinct scents and flavors of cured meats. A study of BCAT from Lactococcus lactis by Yvon, Chambellon et al., found the ideal conditions for the bacterial isozyme as follows: (See Template:Leucine metabolism in humans – this diagram does not include

962-405: The direction being determined by which of the reactants are in excess. This reversibility can be exploited for synthetic chemistry applications to achieve the synthesis of valuable chiral amines. The specific enzymes are named from one of the reactant pairs, for example; the reaction between glutamic acid and pyruvic acid to make alpha ketoglutaric acid and alanine is called alanine transaminase and

999-461: The glutamate and GABA metabolic pathway. The bacteria L. lactis is the primary bacteria responsible for the ripening of cheeses, and the enzymes within the bacteria play key roles in the development of flavor, texture, and aroma profiles. The branched-chain amino acid aminotransferases help to produce compounds like isovaleric acid, isobutyric acid, 2- and 3-methylbutan(al)(ol) and 2-methylpropan(al)(ol) that impart fruity or malty aromas depending on

1036-458: The human and yeast ( Saccharomyces cerevisiae) isoforms. BCAT1 is located in the mitochondria, BCAT2, 3, and 5 are located in chloroplasts, and BCAT4 and 6 are located in the cytoplasm of A. thaliana . However, studies of BCATs in Solanum tuberosum (potato) revealed two isoforms that are 683 (BCAT1) and 746 (BCAT2) bp long located primarily in chloroplasts. In bacteria, there is only one isoform of

1073-407: The mammalian active site contains three surfaces: surface A (Phe75, Tyr207 and Thr240), surface B (Phe30, Tyr141, and Ala314), and surface C (Tyr70, Leu153 and Val155, located on the opposite domain) that bind to the substrate in a Van der Waals-type interaction with the branched side chains of the amino acid substrates. BCATs in mammals catalyze the first step in branched-chain amino acid metabolism,

1110-484: The pathway for β-leucine synthesis via leucine 2,3-aminomutase) Aminotransferase An amino acid contains an amino (NH 2 ) group. A keto acid contains a keto (=O) group. In transamination , the NH 2 group on one molecule is exchanged with the =O group on the other molecule. The amino acid becomes a keto acid, and the keto acid becomes an amino acid. Transaminases require the coenzyme pyridoxal phosphate , which

1147-613: The production of various amino acids, and measuring the concentrations of various transaminases in the blood is important in the diagnosing and tracking many diseases . For example, the presence of elevated transaminases can be an indicator of liver and cardiac damage. Two important transaminase enzymes are aspartate transaminase (AST), also known as serum glutamic oxaloacetic transaminase (SGOT); and alanine transaminase (ALT), also called alanine aminotransferase (ALAT) or serum glutamate-pyruvate transaminase (SGPT). These transaminases were discovered in 1954 and their clinical importance

Branched-chain amino acid aminotransferase - Misplaced Pages Continue

1184-450: The reversible transamination of branched-chain alpha-keto acids (BCKAs) to the branched-chain amino acids (BCAAs) valine , leucine and isoleucine , which are essential for cell growth. In humans, its primary role is the deamination of BCAAs, as humans lack the enzymes for de novo synthesis of BCKAs. The respective cosubstrates are alpha-ketoglutarate and glutamate . The respective reactions are: Cells can further degrade BCKAs by

1221-427: The right of branched chain amino acid aminotransferase was found using X-ray diffraction with a resolution of 2.20 Å. The branched-chain amino acid aminotransferase found in this image was isolated from mycobacteria . This protein is made up of two identical polypeptide chains , totaling 372 residues. The biological function of branched-chain amino acid aminotransferases is to catalyse the synthesis or degradation of

1258-459: The solvent the chromatogram is then treated with ninhydrin to locate the spots. . Animals must metabolize proteins to amino acids, at the expense of muscle tissue, when blood sugar is low. The preference of liver transaminases for oxaloacetate or alpha-ketoglutarate plays a key role in funneling nitrogen from amino acid metabolism to aspartate and glutamate for conversion to urea for excretion of nitrogen. In similar manner, in muscles

1295-466: The use of pyruvate for transamination gives alanine , which is carried by the bloodstream to the liver (the overall reaction being termed glucose-alanine cycle ). Here other transaminases regenerate pyruvate, which provides a valuable precursor for gluconeogenesis . This alanine cycle is analogous to the Cori cycle , which allows anaerobic metabolism by muscles. The transaminase enzymes are important in

1332-473: Was described in 1955. Branched chain amino acid transaminase 1 2ABJ , 2COG , 2COI , 2COJ 586 12035 ENSG00000060982 ENSMUSG00000030268 P54687 P24288 NM_001178091 NM_001178092 NM_001178093 NM_001178094 NM_005504 NM_001024468 NM_007532 NP_001171562 NP_001171563 NP_001171564 NP_001171565 NP_005495 NP_001019639 NP_031558 Branched chain amino acid transaminase 1

1369-461: Was originally called glutamic-pyruvic transaminase or GPT for short. Tissue transaminase activities can be investigated by incubating a homogenate with various amino/keto acid pairs. Transamination is demonstrated if the corresponding new amino acid and keto acid are formed, as revealed by paper chromatography. Reversibility is demonstrated by using the complementary keto/amino acid pair as starting reactants. After chromatogram has been taken out of

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