Aminotransferases leucine aminotransferase

KYNURENINE AMINOTRANSFERASE LEUCINE AMINOTRANSFERASE LYSINE 2,3-AMINOMUTASE LYSINE 6-AMINOTRANSFERASE LYSINE DECARBOXYLASE METHIONINE y-LYASE ORNITHINE AMINOTRANSFERASE PHENYLALANINE DECARBOXYLASE PHOSPHATIDYLSERINE DECARBOXYLASE... 

Amino acid metabolism A artate aminotransferase Alanine aminotransferase Cysteine aminotransferase Tyrosine aminotransferase Leucine aminotransferase Alanine-ketoacid aminotransfoase Ornithine-ketoacid aminotransferase A artate carbamoyl transferase Methionine adenosyl transferase Glutamate decarboxylase Glutamate dehydrogenase Serine hydroxymethyltransferase Aminoacyl-sRNA synthetases... 

The reactions are catalysed by enzymes known as aminotransferases (formerly known as transaminases). For the above reactions, they are (i) aspartate aminotransferase, (ii) alanine aminotransferase and (iii) leucine aminotransferase. Details of these reactions can be found in Appendix 8.4. 

This enzyme [EC 2.6.1.42], also referred to as transaminase B, catalyzes the reversible reaction of leucine with a-ketoglutarate (or, 2-oxoglutarate) to produce 4-methyl-2-oxopentanoate and glutamate. The pyridoxal-phosphate-dependent enzyme will also utilize isoleucine and valine as substrates. However, this enzyme is distinct from that of valine pyruvate aminotransferase [EC 2.6.1.66]. See also Leucine Aminotransferase... 

GLUTAMATE DEHYDROGENASE GLUTAMATE SYNTHASE a-KETOGLUTARATE DEHYDROGENASE LEUCINE AMINOTRANSFERASE LYSINE 6-AMINOTRANSFERASE LYSYL HYDROXYLASE... 

LEUCINE 2,3-AMINOMUTASE LEUCINE AMINOTRANSFERASE LEUCINE DEHYDROGENASE LEUCINE KINETICS LEUCYL-tRNA SYNTHETASE ZWITTERION yS-Leucine,... 

LEUCINE 2,3-AMINOMUTASE LEUCINE AMINOPEPTIDASE LEUCINE AMINOTRANSFERASE... 

BRANCHED-CHAIN AMINO ACID AMINOTRANSFERASE LEUCINE DEHYDROGENASE LEUCINE KINETICS RROTEIN TURNOVER KINETICS SAAM... 

LEUCINE AMINOTRANSFERASE LEUCINE DEHYDROGENASE LEUCINE KINETICS... 

Ahpiperidine-2,6-dicarboxylate dehydrogenase (Q) N-succinyl-2-amino-6-ketopimelate synthase succinyl diaminopimelate aminotransferase succinyl diaminopimelate desuccinylase diaminopimelate epimerase diaminopimelate decarboxylase (Q threonine dehydratase (serine dehydratase) acetolactate synthase acetohydroxy acid isomeroreductase dihydroxy acid dehydratase valine aminotransferase a-isopropylmalate synthase isopropylmalate isomerase -isopropylmalate dehydrogenase leucine aminotransferase... 

Aminopeptidase, cytosol Aminopeptidase, leucine Aminopropyltransferase, putrescine Aminotransferase Aminotransferase, alanine Aminotransferase, aspartate Aminotransferase, glutamate-glyoxylate Aminotransferase, ornithine-keto acid Aminotransferase, serine-glyoxylate Ammonia... 

Biosynthesis Leu is formed from pyruvic acid - 2-acetolactic acid [acetolactate synthase (EC 4.1.3.18.)+(l-hydroxyethyl)-TPP] - 2,3-dihydroxy-isovaleric acid [reductase+NAD(P)H] - 2-oxoisova-leric acid [dihydroxyacid dehydratase] - 2-isopropyl-malate [2-isopropylmalate synthase + acetyl-CoA (EC 4.1.3.12)] -> 3-isopropylmalate [isopropylmalate dehydratase (EC 4.2.1.33) -HjO+HiO] 2-oxo-isocaproate [3-isopropylmalate dehydrogenase (EC 1.1.1.85) + NAD ] L. [leucine aminotransferase (EC... 

Isopropylmalate synthase 2 isopropylmalate isomerase 3 carboxyhydroxyisocaproate decarboxylase 4 leucine aminotransferase... 

FIGURE 4.6 Conversion of amino acids into aroma components of banana as illnstrated by leucine. Ej, L-leucine aminotransferase E2, pyruvate decarboxylase E3, aldehyde dehydrogenase ThPP, thiamin pyrophosphate oxidized lipoic acid reduced lipoic acid FAD flavin-adenine dinucleotide NAD-i-, oxidized nicotinamide-adenine dinucleotide CoA-SH, coenzyme A. (From Drawert, F., Amma Research, H. Maarse, P.J. Groenen, Eds., Pudoc, Wageningen, 1975, p. 245. With permission.)... 

Methyl-2-oxopentanoate =iL-leucine Leucine aminotransferase L-Glutamate... 

Transaminase enzymes (also called aminotransferases) specifically use 2-oxoglutarate as the amino group acceptor to generate glutamate but some have a wide specificity with respect to the amino donor. For example, the three branched-chain amino acids leucine, isoleucine and valine, all serve as substrates for the same enzyme, branched-chain amino acid transaminase, BCAAT ... 

This enzyme [EC 2.6.1.21], also known as D-aspartate aminotransferase, D-amino acid aminotransferase, and D-amino acid transaminase, catalyzes the reversible pyridoxal-phosphate-dependent reaction of D-alanine with a-ketoglutarate to yield pyruvate and D-glutamate. The enzyme will also utilize as substrates the D-stereoisomers of leucine, aspartate, glutamate, aminobutyrate, norva-hne, and asparagine. See o-Amino Acid Aminotransferase... 

See specific aminotransferase Glutamate as a substrate or product, GLUTAMATE DECARBOXYLASE GLUTAMATE DEHYDROGENASE GLUTAMATE SYNTHASE GLUTAMINE SYNTHETASE y-GLUTAMYL TRANSPEPTIDASE LEUCINE AMINOTRANSEERASE LYSINE 6-AMINOTRANSEERASE... 

Free amino acids are further catabolized into several volatile flavor compounds. However, the pathways involved are not fully known. A detailed summary of the various studies on the role of the catabolism of amino acids in cheese flavor development was published by Curtin and McSweeney (2004). Two major pathways have been suggested (1) aminotransferase or lyase activity and (2) deamination or decarboxylation. Aminotransferase activity results in the formation of a-ketoacids and glutamic acid. The a-ketoacids are further degraded to flavor compounds such as hydroxy acids, aldehydes, and carboxylic acids. a-Ketoacids from methionine, branched-chain amino acids (leucine, isoleucine, and valine), or aromatic amino acids (phenylalanine, tyrosine, and tryptophan) serve as the precursors to volatile flavor compounds (Yvon and Rijnen, 2001). Volatile sulfur compounds are primarily formed from methionine. Methanethiol, which at low concentrations, contributes to the characteristic flavor of Cheddar cheese, is formed from the catabolism of methionine (Curtin and McSweeney, 2004 Weimer et al., 1999). Furthermore, bacterial lyases also metabolize methionine to a-ketobutyrate, methanethiol, and ammonia (Tanaka et al., 1985). On catabolism by aminotransferase, aromatic amino acids yield volatile flavor compounds such as benzalde-hyde, phenylacetate, phenylethanol, phenyllactate, etc. Deamination reactions also result in a-ketoacids and ammonia, which add to the flavor of... 

Chen and Contario [31] reported an HPLC resolution of enantiomers of vigabatrin. The samples were treated with N-f-butoxycarbonyl-L-leucine N-hdroxysuccinimide esters in the presence of sodium carbonate and then with trifluoroacetic acid. The resulting diastereoisomers were separated on a column (25 cm x 4 mm) of Lichrosorb RP-8 (10 fim) with acetonitrile-dioxan-0.5 M H3PO4 (pH 7)-acetonitrile (24 1) as mobile phase with a flow rate of 2 ml/min and detection at 210 nm. Good recoveries of the inactive R-(—)-form (0.5-2%) added to the active S-(+)-form of the aminobutyrate aminotransferase inhibitor were obtained. The results on a sample containing 0.24% of the R-(—)-form agreed with those obtained by GC. 

In all cases the keto acids seem to be formed by typical a-ketogluta-rate-linked, pyridoxal phosphate-dependent transaminases (EC 2.6.1.6, etc.) (9, 154, 156, 157). There has been little study of isolated, presumably specific enzymes in connection with flavors, although the leucine and alanine aminotransferases of tomato have been precipitated with (NH4)oS04 (164, 165). Transaminase activity in Saccharomyces cere-visiae has a pH optimum of 7.2 (154), and a-ketoglutarate is the only amino group recipient (154, 166). Only aspartate and amino acids with hydrophobic side chains are acted on (154). 

Fahien, L. A., Krniotek, E. H., Woldegiorgis, C., Evenson, M., Shrago, E., and Marshall, M. (1985). Regulation of aminotransferase-glutamate dehydrogenase interactions by car-bamy] phosphate synthaSe, I, Mg plus leucine versus citrate and malate- /. fijof- Otem. 260, 6069 79,... 

A number of amino acids, like alanine, leucine, tyrosine, aspartic acid, cystein and arginine react with a-ketoacids and transfer their a-amino group to the a-carb-on of the a-keto acids. These reactions are catalysed by the enzyme called transaminase or aminotransferase. For example, transfer of the amino group of aspartic acid (14) to a-ketoglutaric acid (23) gives glutamic acid (16) and oxaloacetic acid (24). 

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