The Enzyme Database

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EC 1.1.1.85     
Accepted name: 3-isopropylmalate dehydrogenase
Reaction: (2R,3S)-3-isopropylmalate + NAD+ = 4-methyl-2-oxopentanoate + CO2 + NADH + H+ (overall reaction)
(1a) (2R,3S)-3-isopropylmalate + NAD+ = (2S)-2-isopropyl-3-oxosuccinate + NADH + H+
(1b) (2S)-2-isopropyl-3-oxosuccinate = 4-methyl-2-oxopentanoate + CO2 (spontaneous)
For diagram of leucine biosynthesis, click here
Other name(s): β-isopropylmalic enzyme; β-isopropylmalate dehydrogenase; threo-Ds-3-isopropylmalate dehydrogenase; 3-carboxy-2-hydroxy-4-methylpentanoate:NAD+ oxidoreductase
Systematic name: (2R,3S)-3-isopropylmalate:NAD+ oxidoreductase
Comments: The product decarboxylates spontaneously to yield 4-methyl-2-oxopentanoate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9030-97-1
References:
1.  Burns, R.O., Umbarger, H.E. and Gross, S.R. The biosynthesis of leucine. III. The conversion of α-hydroxy-β-carboxyisocaproate to α-ketoisocaproate. Biochemistry 2 (1963) 1053. [PMID: 14087358]
2.  Parsons, S.J. and Burns, R.O. Purification and properties of β-isopropylmalate dehydrogenase. J. Biol. Chem. 244 (1969) 996–1003. [PMID: 4889950]
3.  Németh, A., Svingor, Á., Pócsik, M., Dobó, J., Magyar, C, Szilaaagyi, A., Gál, P. and Závodszky, P. Mirror image mutations reveal the significance of an intersubunit ion cluster in the stability of 3-isopropylmalate dehydrogenase. FEBS Lett. 468 (2000) 48–52. [DOI] [PMID: 10683439]
4.  Calvo, J. M., Stevens, C. M., Kalyanpur, M. G., and Umbarger, H. E. The absolute configuration of α-hydroxy-β-carboxyisocaproic acid (3-isopropylmalic acid), an intermediate in leucine biosynthesis. Biochemistry 3 (1964) 2024–2027. [PMID: 14269331]
[EC 1.1.1.85 created 1972, modified 1976]
 
 
EC 1.2.4.4     
Accepted name: 3-methyl-2-oxobutanoate dehydrogenase (2-methylpropanoyl-transferring)
Reaction: 3-methyl-2-oxobutanoate + [dihydrolipoyllysine-residue (2-methylpropanoyl)transferase] lipoyllysine = [dihydrolipoyllysine-residue (2-methylpropanoyl)transferase] S-(2-methylpropanoyl)dihydrolipoyllysine + CO2
For diagram of oxo-acid-dehydrogenase complexes, click here
Glossary: dihydrolipoyl group
thiamine diphosphate = 3-[(4-amino-2-methylpyrimidin-5-yl)methyl]-5-(2-diphosphoethyl)-4-methyl-1,3-thiazolium
Other name(s): 2-oxoisocaproate dehydrogenase; 2-oxoisovalerate (lipoate) dehydrogenase; 3-methyl-2-oxobutanoate dehydrogenase (lipoamide); 3-methyl-2-oxobutanoate:lipoamide oxidoreductase (decarboxylating and acceptor-2-methylpropanoylating); α-keto-α-methylvalerate dehydrogenase; α-ketoisocaproate dehydrogenase; α-ketoisocaproic dehydrogenase; α-ketoisocaproic-α-keto-α-methylvaleric dehydrogenase; α-ketoisovalerate dehydrogenase; α-oxoisocaproate dehydrogenase; BCKDH (ambiguous); BCOAD; branched chain keto acid dehydrogenase; branched-chain (-2-oxoacid) dehydrogenase (BCD); branched-chain 2-keto acid dehydrogenase; branched-chain 2-oxo acid dehydrogenase; branched-chain α-keto acid dehydrogenase; branched-chain α-oxo acid dehydrogenase; branched-chain keto acid dehydrogenase; branched-chain ketoacid dehydrogenase; dehydrogenase, 2-oxoisovalerate (lipoate); dehydrogenase, branched chain α-keto acid
Systematic name: 3-methyl-2-oxobutanoate:[dihydrolipoyllysine-residue (2-methylpropanoyl)transferase]-lipoyllysine 2-oxidoreductase (decarboxylating, acceptor-2-methylpropanoylating)
Comments: Contains thiamine diphosphate. It acts not only on 3-methyl-2-oxobutanaoate, but also on 4-methyl-2-oxopentanoate and (S)-3-methyl-2-oxopentanoate, so that it acts on the 2-oxo acids that derive from the action of transaminases on valine, leucine and isoleucine. It is a component of the multienzyme 3-methyl-2-oxobutanoate dehydrogenase complex in which multiple copies of it are bound to a core of molecules of EC 2.3.1.168, dihydrolipoyllysine-residue (2-methylpropanoyl)transferase, which also binds multiple copies of EC 1.8.1.4, dihydrolipoyl dehydrogenase. It does not act on free lipoamide or lipoyllysine, but only on the lipoyllysine residue in EC 2.3.1.168.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9082-72-8
References:
1.  Bowden, J.A. and Connelly, J.L. Branched chain α-keto acid metabolism. II. Evidence for the common identity of α-ketoisocaproic acid and α-keto-β-methyl-valeric acid dehydrogenases. J. Biol. Chem. 243 (1968) 3526–3531. [PMID: 5656388]
2.  Connelly, J.L., Danner, D.J. and Bowden, J.A. Branched chain α-keto acid metabolism. I. Isolation, purification, and partial characterization of bovine liver α-ketoisocaproic:α-keto-β-methylvaleric acid dehydrogenase. J. Biol. Chem. 243 (1968) 1198–1203. [PMID: 5689906]
3.  Danner, D.J., Lemmon, S.K., Beharse, J.C. and Elsas, L.J., II Purification and characterization of branched chain α-ketoacid dehydrogenase from bovine liver mitochondria. J. Biol. Chem. 254 (1979) 5522–5526. [PMID: 447664]
4.  Pettit, F.H., Yeaman, S.J. and Reed, L.J. Purification and characterization of branched chain α-keto acid dehydrogenase complex of bovine kidney. Proc. Natl. Acad. Sci. USA 75 (1978) 4881–4885. [DOI] [PMID: 283398]
5.  Perham, R.N. Swinging arms and swinging domains in multifunctional enzymes: catalytic machines for multistep reactions. Annu. Rev. Biochem. 69 (2000) 961–1004. [DOI] [PMID: 10966480]
[EC 1.2.4.4 created 1972 (EC 1.2.4.3 created 1972, incorporated 1978), modified 2003]
 
 
EC 2.3.1.182      
Transferred entry: (R)-citramalate synthase. Now classified as EC 2.3.3.21, (R)-citramalate synthase.
[EC 2.3.1.182 created 2007, deleted 2021]
 
 
EC 2.3.3.21     
Accepted name: (R)-citramalate synthase
Reaction: acetyl-CoA + pyruvate + H2O = CoA + (2R)-2-hydroxy-2-methylbutanedioate
Glossary: (2R)-2-hydroxy-2-methylbutanedioate = (2R)-2-methylmalate = (–)-citramalate
3-methyl-2-oxobutanoate = α-ketoisovalerate
2-oxobutanoate = α-ketobutyrate
4-methyl-2-oxopentanoate = α-ketoisocaproate
2-oxohexanoate = α-ketopimelate
2-oxoglutarate = α-ketoglutarate
Other name(s): CimA
Comments: One of the enzymes involved in a pyruvate-derived pathway for isoleucine biosynthesis that is found in some bacterial and archaeal species [1,2]. The enzyme can be inhibited by isoleucine, the end-product of the pathway, but not by leucine [2]. The enzyme is highly specific for pyruvate as substrate, as the 2-oxo acids 3-methyl-2-oxobutanoate, 2-oxobutanoate, 4-methyl-2-oxopentanoate, 2-oxohexanoate and 2-oxoglutarate cannot act as substrate [1,2].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Howell, D.M., Xu, H. and White, R.H. (R)-citramalate synthase in methanogenic archaea. J. Bacteriol. 181 (1999) 331–333. [DOI] [PMID: 9864346]
2.  Xu, H., Zhang, Y., Guo, X., Ren, S., Staempfli, A.A., Chiao, J., Jiang, W. and Zhao, G. Isoleucine biosynthesis in Leptospira interrogans serotype 1ai strain 56601 proceeds via a threonine-independent pathway. J. Bacteriol. 186 (2004) 5400–5409. [DOI] [PMID: 15292141]
[EC 2.3.3.21 created 2007 as EC 2.3.1.182, transferred 2021 to EC 2.3.3.21]
 
 
EC 2.6.1.28     
Accepted name: tryptophan—phenylpyruvate transaminase
Reaction: L-tryptophan + phenylpyruvate = (indol-3-yl)pyruvate + L-phenylalanine
For diagram of reaction, click here and for mechanism, click here
Other name(s): L-tryptophan-α-ketoisocaproate aminotransferase
Systematic name: L-tryptophan:phenylpyruvate aminotransferase
Comments: Valine, leucine and isoleucine can replace tryptophan as amino donor.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 37277-87-5
References:
1.  Koide, Y., Honma, M. and Shimomura, T. L-Tryptophan-α-ketoisocaproate aminotransferase from Pseudomonas sp. Agric. Biol. Chem. 44 (1980) 2013–2019.
2.  Sukanya, N.K. and Vaidyanathan, C.S. Aminotransferases of Agrobacterium tumefaciens. Transamination between tryptophan and phenylpyruvate. Biochem. J. 92 (1964) 594–598. [PMID: 5837443]
[EC 2.6.1.28 created 1972]
 
 


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