The Enzyme Database

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EC 1.1.1.84     
Accepted name: dimethylmalate dehydrogenase
Reaction: (R)-3,3-dimethylmalate + NAD+ = 3-methyl-2-oxobutanoate + CO2 + NADH
For diagram of pantothenate catabolism, click here
Other name(s): β,β-dimethylmalate dehydrogenase
Systematic name: (R)-3,3-dimethylmalate:NAD+ oxidoreductase (decarboxylating)
Comments: Requires K+ or NH4+ and Mn2+ or Co2+; also acts on (R)-malate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 37250-21-8
References:
1.  Magee, P.T. and Snell, E.E. The bacterial degradation of pantothenic acid. IV. Enzymatic conversion of aldopantoate to α-ketoisovalerate. Biochemistry 5 (1966) 409–416. [PMID: 4287371]
[EC 1.1.1.84 created 1972]
 
 
EC 1.2.1.25     
Accepted name: branched-chain α-keto acid dehydrogenase system
Reaction: 3-methyl-2-oxobutanoate + CoA + NAD+ = 2-methylpropanoyl-CoA + CO2 + NADH
Other name(s): branched-chain α-keto acid dehydrogenase complex; 2-oxoisovalerate dehydrogenase; α-ketoisovalerate dehydrogenase; 2-oxoisovalerate dehydrogenase (acylating)
Systematic name: 3-methyl-2-oxobutanoate:NAD+ 2-oxidoreductase (CoA-methylpropanoylating)
Comments: This enzyme system catalyses the oxidative decarboxylation of branched-chain α-keto acids derived from L-leucine, L-isoleucine, and L-valine to branched-chain acyl-CoAs. It belongs to the 2-oxoacid dehydrogenase system family, which also includes EC 1.2.1.104, pyruvate dehydrogenase system, EC 1.2.1.105, 2-oxoglutarate dehydrogenase system, EC 1.4.1.27, glycine cleavage system, and EC 2.3.1.190, acetoin dehydrogenase system. With the exception of the glycine cleavage system, which contains 4 components, the 2-oxoacid dehydrogenase systems share a common structure, consisting of three main components, namely a 2-oxoacid dehydrogenase (E1), a dihydrolipoamide acyltransferase (E2), and dihydrolipoamide dehydrogenase (E3). The reaction catalysed by this system is the sum of three activities: EC 1.2.4.4, 3-methyl-2-oxobutanoate dehydrogenase (2-methylpropanoyl-transferring), EC 2.3.1.168, dihydrolipoyllysine-residue (2-methylpropanoyl)transferase, and EC 1.8.1.4, dihydrolipoyl dehydrogenase. The system also acts on (S)-3-methyl-2-oxopentanoate and 4-methyl-2-oxopentanoate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 37211-61-3
References:
1.  Namba, Y., Yoshizawa, K., Ejima, A., Hayashi, T. and Kaneda, T. Coenzyme A- and nicotinamide adenine dinucleotide-dependent branched chain α-keto acid dehydrogenase. I. Purification and properties of the enzyme from Bacillus subtilis. J. Biol. Chem. 244 (1969) 4437–4447. [PMID: 4308861]
2.  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]
3.  Harris, R.A., Hawes, J.W., Popov, K.M., Zhao, Y., Shimomura, Y., Sato, J., Jaskiewicz, J. and Hurley, T.D. Studies on the regulation of the mitochondrial α-ketoacid dehydrogenase complexes and their kinases. Adv. Enzyme Regul. 37 (1997) 271–293. [DOI] [PMID: 9381974]
4.  Evarsson, A., Chuang, J.L., Wynn, R.M., Turley, S., Chuang, D.T. and Hol, W.G. Crystal structure of human branched-chain α-ketoacid dehydrogenase and the molecular basis of multienzyme complex deficiency in maple syrup urine disease. Structure 8 (2000) 277–291. [PMID: 10745006]
5.  Reed, L.J. A trail of research from lipoic acid to α-keto acid dehydrogenase complexes. J. Biol. Chem. 276 (2001) 38329–38336. [DOI] [PMID: 11477096]
[EC 1.2.1.25 created 1972, modified 2019, modified 2020]
 
 
EC 1.2.1.33     
Accepted name: (R)-dehydropantoate dehydrogenase
Reaction: (R)-4-dehydropantoate + NAD+ + H2O = (R)-3,3-dimethylmalate + NADH + 2 H+
For diagram of pantothenate catabolism, click here
Other name(s): D-aldopantoate dehydrogenase; D-2-hydroxy-3,3-dimethyl-3-formylpropionate:diphosphopyridine nucleotide (DPN+) oxidoreductase
Systematic name: (R)-4-dehydropantoate:NAD+ 4-oxidoreductase
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 37250-96-7
References:
1.  Magee, P.T. and Snell, E.E. The bacterial degradation of pantothenic acid. IV. Enzymatic conversion of aldopantoate to α-ketoisovalerate. Biochemistry 5 (1966) 409–416. [PMID: 4287371]
[EC 1.2.1.33 created 1972]
 
 
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 2.1.2.11     
Accepted name: 3-methyl-2-oxobutanoate hydroxymethyltransferase
Reaction: 5,10-methylenetetrahydrofolate + 3-methyl-2-oxobutanoate + H2O = tetrahydrofolate + 2-dehydropantoate
For diagram of the early stages of CoA biosynthesis, click here
Other name(s): α-ketoisovalerate hydroxymethyltransferase; dehydropantoate hydroxymethyltransferase; ketopantoate hydroxymethyltransferase; oxopantoate hydroxymethyltransferase; 5,10-methylene tetrahydrofolate:α-ketoisovalerate hydroxymethyltransferase
Systematic name: 5,10-methylenetetrahydrofolate:3-methyl-2-oxobutanoate hydroxymethyltransferase
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 56093-17-5
References:
1.  Powers, S.G. and Snell, E.E. Ketopantoate hydroxymethyltransferase. II. Physical, catalytic, and regulatory properties. J. Biol. Chem. 251 (1976) 3786–3793. [PMID: 6463]
2.  Teller, J.H., Powers, S.G. and Snell, E.E. Ketopantoate hydroxymethyltransferase. I. Purification and role in pantothenate biosynthesis. J. Biol. Chem. 251 (1976) 3780–3785. [PMID: 776976]
[EC 2.1.2.11 created 1982]
 
 
EC 2.3.1.182     
Accepted name: (R)-citramalate synthase
Reaction: acetyl-CoA + pyruvate + H2O = CoA + (2R)-2-hydroxy-2-methylbutanedioate
Glossary: (-)-citramalate = (2R)-2-methylmalate = (2R)-2-hydroxy-2-methylbutanedioate
α-ketoisovalerate = 3-methyl-2-oxobutanoate
α-ketobutyrate = 2-oxobutanoate
α-ketoisocaproate = 4-methyl-2-oxopentanoate
α-ketopimelate = 2-oxohexanoate
α-ketoglutarate = 2-oxoglutarate
Other name(s): CimA
Comments: One of the enzymes involved in a novel pyruvate pathway for isoleucine biosynthesis that is found in some, mainly archaeal, bacteria [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. [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 2.3.1.182 created 2007]
 
 
EC 2.6.1.66     
Accepted name: valine—pyruvate transaminase
Reaction: L-valine + pyruvate = 3-methyl-2-oxobutanoate + L-alanine
For diagram of reaction, click here, of isoleucine and valine biosynthesis, click here and for diagram of mechanism, click here
Other name(s): transaminase C; valine-pyruvate aminotransferase; alanine-oxoisovalerate aminotransferase
Systematic name: L-valine:pyruvate aminotransferase
Comments: Different from EC 2.6.1.42, branched-chain-amino-acid-transaminase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 73379-50-7
References:
1.  Falkinham, J.O. , III Identification of a mutation affecting an alanine-α-ketoisovalerate transaminase activity in Escherichia coli K-12. Mol. Gen. Genet. 176 (1979) 147–149. [PMID: 396446]
2.  Rudman, D. and Meister, A. Transamination in Escherichia coli. J. Biol. Chem. 200 (1953) 591–604. [PMID: 13034817]
[EC 2.6.1.66 created 1984]
 
 
EC 4.1.1.72     
Accepted name: branched-chain-2-oxoacid decarboxylase
Reaction: (3S)-3-methyl-2-oxopentanoate = 2-methylbutanal + CO2
Other name(s): branched-chain oxo acid decarboxylase; branched-chain α-keto acid decarboxylase; branched-chain keto acid decarboxylase; BCKA; (3S)-3-methyl-2-oxopentanoate carboxy-lyase
Systematic name: (3S)-3-methyl-2-oxopentanoate carboxy-lyase (2-methylbutanal-forming)
Comments: Acts on a number of 2-oxo acids, with a high affinity towards branched-chain substrates. The aldehyde formed may be enzyme-bound, and may be an intermediate in the bacterial system for the biosynthesis of branched-chain fatty acids.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 63653-19-0
References:
1.  Oku, H. and Kaneda, T. Biosynthesis of branched-chain fatty acids in Bacillus subtilis. A decarboxylase is essential for branched-chain fatty acid synthetase. J. Biol. Chem. 263 (1988) 18386–18396. [PMID: 3142877]
2.  de la Plaza, M., Fernandez de Palencia, P., Pelaez, C. and Requena, T. Biochemical and molecular characterization of α-ketoisovalerate decarboxylase, an enzyme involved in the formation of aldehydes from amino acids by Lactococcus lactis. FEMS Microbiol. Lett. 238 (2004) 367–374. [PMID: 15358422]
3.  Smit, B.A., van Hylckama Vlieg, J.E., Engels, W.J., Meijer, L., Wouters, J.T. and Smit, G. Identification, cloning, and characterization of a Lactococcus lactis branched-chain α-keto acid decarboxylase involved in flavor formation. Appl. Environ. Microbiol. 71 (2005) 303–311. [PMID: 15640202]
[EC 4.1.1.72 created 1990]
 
 


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