The Enzyme Database

Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB)

Proposed Changes to the Enzyme List

The entries below are proposed additions and amendments to the Enzyme Nomenclature list. They were prepared for the NC-IUBMB by Kristian Axelsen, Richard Cammack, Ron Caspi, Masaaki Kotera, Andrew McDonald, Gerry Moss, Dietmar Schomburg, Ida Schomburg and Keith Tipton. Comments and suggestions on these draft entries should be sent to Dr Andrew McDonald (Department of Biochemistry, Trinity College Dublin, Dublin 2, Ireland). The date on which an enzyme will be made official is appended after the EC number. To prevent confusion please do not quote new EC numbers until they are incorporated into the main list.

An asterisk before 'EC' indicates that this is an amendment to an existing enzyme rather than a new enzyme entry.


Contents

*EC 1.1.1.261 sn-glycerol-1-phosphate dehydrogenase
EC 1.14.13.107 limonene 1,2-monooxygenase
EC 1.14.14.6 methanesulfonate monooxygenase
*EC 1.17.1.2 4-hydroxy-3-methylbut-2-enyl diphosphate reductase
EC 1.17.4.3 transferred
EC 1.17.7 With an iron-sulfur protein as acceptor
EC 1.17.7.1 (E)-4-hydroxy-3-methylbut-2-enyl-diphosphate synthase (ferredoxin)
EC 2.3.1.70 deleted
*EC 2.5.1.41 phosphoglycerol geranylgeranyltransferase
*EC 2.5.1.42 geranylgeranylglycerol-phosphate geranylgeranyltransferase
EC 2.7.7.67 CDP-2,3-bis-(O-geranylgeranyl)-sn-glycerol synthase
EC 4.2.1.114 methanogen homoaconitase
EC 4.2.1.115 UDP-N-acetylglucosamine 4,6-dehydratase (configuration-inverting)
EC 4.2.3.38 α-bisabolene synthase
EC 4.2.3.39 epi-cedrol synthase
EC 4.2.3.40 (Z)-γ-bisabolene synthase


*EC 1.1.1.261
Accepted name: sn-glycerol-1-phosphate dehydrogenase
Reaction: sn-glycerol 1-phosphate + NAD(P)+ = glycerone phosphate + NAD(P)H + H+
For diagram of archaetidylserine biosynthesis, click here
Glossary: glycerone phosphate = dihydroxyacetone phosphate = 3-hydroxy-2-oxopropyl phosphate
Other name(s): glycerol-1-phosphate dehydrogenase [NAD(P)+]; sn-glycerol-1-phosphate:NAD+ oxidoreductase; G-1-P dehydrogenase; Gro1PDH; AraM
Systematic name: sn-glycerol-1-phosphate:NAD(P)+ 2-oxidoreductase
Comments: This enzyme is found primarily as a Zn2+-dependent form in archaea but a Ni2+-dependent form has been found in Gram-positive bacteria [6]. The Zn2+-dependent metalloenzyme is responsible for the formation of archaea-specific sn-glycerol-1-phosphate, the first step in the biosynthesis of polar lipids in archaea. It is the enantiomer of sn-glycerol 3-phosphate, the form of glycerophosphate found in bacteria and eukaryotes. The other enzymes involved in the biosynthesis of polar lipids in archaea are EC 2.5.1.41 (phosphoglycerol geranylgeranyltransferase) and EC 2.5.1.42 (geranylgeranylglycerol-phosphate geranylgeranyltransferase), which together alkylate the hydroxy groups of glycerol 1-phosphate to give unsaturated archaetidic acid, which is acted upon by EC 2.7.7.67 (CDP-archaeol synthase) to form CDP-unsaturated archaeol. The final step in the pathway involves the addition of L-serine, with concomitant removal of CMP, leading to the production of unsaturated archaetidylserine [4]. Activity of the enzyme is stimulated by K+ [2].
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, CAS registry number: 204594-18-3
References:
1.  Nishihara, M. and Koga, Y. sn-Glycerol-1-phosphate dehydrogenase in Methanobacterium thermoautotrophicum: key enzyme in biosynthesis of the enantiomeric glycerophosphate backbone of ether phospholipids of archaebacteria. J. Biochem. 117 (1995) 933–935. [PMID: 8586635]
2.  Nishihara, M. and Koga, Y. Purification and properties of sn-glycerol-1-phosphate dehydrogenase from Methanobacterium thermoautotrophicum: characterization of the biosynthetic enzyme for the enantiomeric glycerophosphate backbone of ether polar lipids of Archaea. J. Biochem. 122 (1997) 572–576. [PMID: 9348086]
3.  Koga, Y., Kyuragi, T., Nishihara, M. and Sone, N. Did archaeal and bacterial cells arise independently from noncellular precursors? A hypothesis stating that the advent of membrane phospholipid with enantiomeric glycerophosphate backbones caused the separation of the two lines of descent. J. Mol. Evol. 46 (1998) 54–63. [PMID: 9419225]
4.  Morii, H., Nishihara, M. and Koga, Y. CTP:2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate cytidyltransferase in the methanogenic archaeon Methanothermobacter thermoautotrophicus. J. Biol. Chem. 275 (2000) 36568–36574. [PMID: 10960477]
5.  Han, J.S. and Ishikawa, K. Active site of Zn2+-dependent sn-glycerol-1-phosphate dehydrogenase from Aeropyrum pernix K1. Archaea 1 (2005) 311–317. [PMID: 15876564]
6.  Guldan, H., Sterner, R. and Babinger, P. Identification and characterization of a bacterial glycerol-1-phosphate dehydrogenase: Ni(2+)-dependent AraM from Bacillus subtilis. Biochemistry 47 (2008) 7376–7384. [PMID: 18558723]
[EC 1.1.1.261 created 2000, modified 2009]
 
 
EC 1.14.13.107
Accepted name: limonene 1,2-monooxygenase
Reaction: (1) (S)-limonene + NAD(P)H + H+ + O2 = 1,2-epoxymenth-8-ene + NAD(P)+ + H2O
(2) (R)-limonene + NAD(P)H + H+ + O2 = 1,2-epoxymenth-8-ene + NAD(P)+ + H2O
For diagram of limonene catabolism, click here
Glossary: limonene = a monoterpenoid
(S)-limonene = (-)-limonene
(R)-limonene = (+)-limonene
limonene-1,2-epoxide = 1,2-epoxymenth-8-ene = 1-methyl-4-(prop-1-en-2-yl)-7-oxabicyclo[4.1.0]heptane
Systematic name: limonene,NAD(P)H:oxygen oxidoreductase
Comments: A flavoprotein (FAD). Limonene is the most widespread terpene and is formed by more than 300 plants. Rhodococcus erythropolis DCL14, a Gram-positive bacterium, is able to grow on both (S)-limonene and (R)-limonene as the sole source of carbon and energy. NADPH can act instead of NADH, although more slowly. It has not been established if the product formed is optically pure or a mixture of two enantiomers.
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB, UM-BBD
References:
1.  van der Werf, M.J., Swarts, H.J. and de Bont, J.A. Rhodococcus erythropolis DCL14 contains a novel degradation pathway for limonene. Appl. Environ. Microbiol. 65 (1999) 2092–2102. [PMID: 10224006]
[EC 1.14.13.107 created 2009]
 
 
EC 1.14.14.6
Transferred entry: methanesulfonate monooxygenase. Now EC 1.14.13.111, methanesulfonate monooxygenase. Formerly thought to involve FMNH2 but now shown to use NADH.
[EC 1.14.14.6 created 2009, deleted 2010]
 
 
*EC 1.17.1.2
Transferred entry: 4-hydroxy-3-methylbut-2-enyl diphosphate reductase, now classified as EC 1.17.7.4, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase.
[EC 1.17.1.2 created 2003, modified 2009, deleted 2016]
 
 
EC 1.17.4.3
Transferred entry: 4-hydroxy-3-methylbut-2-en-1-yl diphosphate synthase. As ferredoxin and not protein-disulfide is now known to take part in the reaction, the enzyme has been transferred to EC 1.17.7.1, (E)-4-hydroxy-3-methylbut-2-enyl-diphosphate synthase.
[EC 1.17.4.3 created 2003, deleted 2009]
 
 
EC 1.17.7 With an iron-sulfur protein as acceptor
 
EC 1.17.7.1
Accepted name: (E)-4-hydroxy-3-methylbut-2-enyl-diphosphate synthase (ferredoxin)
Reaction: (E)-4-hydroxy-3-methylbut-2-en-1-yl diphosphate + H2O + 2 oxidized ferredoxin = 2-C-methyl-D-erythritol 2,4-cyclodiphosphate + 2 reduced ferredoxin
For diagram of Non-Mevalonate terpenoid biosynthesis, click here
Other name(s): 4-hydroxy-3-methylbut-2-en-1-yl diphosphate synthase (ambiguous); (E)-4-hydroxy-3-methylbut-2-en-1-yl-diphosphate:protein-disulfide oxidoreductase (hydrating) (incorrect); (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase (ambiguous); gcpE (gene name); ISPG (gene name); (E)-4-hydroxy-3-methylbut-2-enyl-diphosphate synthase
Systematic name: (E)-4-hydroxy-3-methylbut-2-en-1-yl-diphosphate:oxidized ferredoxin oxidoreductase
Comments: An iron-sulfur protein found in plant chloroplasts and cyanobacteria that contains a [4Fe-4S] cluster [1]. Forms part of an alternative non-mevalonate pathway for isoprenoid biosynthesis. Bacteria have a similar enzyme that uses flavodoxin rather than ferredoxin (cf. EC 1.17.7.3). The enzyme from the plant Arabidopsis thaliana is active with photoreduced 5-deazaflavin but not with flavodoxin [1].
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB
References:
1.  Okada, K. and Hase, T. Cyanobacterial non-mevalonate pathway: (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase interacts with ferredoxin in Thermosynechococcus elongatus BP-1. J. Biol. Chem. 280 (2005) 20672–20679. [PMID: 15792953]
2.  Seemann, M., Wegner, P., Schünemann, V., Tse Sum Bui, B., Wolff, M., Marquet, A., Trautwein, A.X. and Rohmer, M. Isoprenoid biosynthesis in chloroplasts via the methylerythritol phosphate pathway: the (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase (GcpE) from Arabidopsis thaliana is a [4Fe-4S] protein. J. Biol. Inorg. Chem. 10 (2005) 131–137. [PMID: 15650872]
3.  Seemann, M., Tse Sum Bui, B., Wolff, M., Tritsch, D., Campos, N., Boronat, A., Marquet, A. and Rohmer, M. Isoprenoid biosynthesis through the methylerythritol phosphate pathway: the (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase (GcpE) is a [4Fe-4S] protein. Angew. Chem. Int. Ed. Engl. 41 (2002) 4337–4339. [PMID: 12434382]
4.  Seemann, M., Tse Sum Bui, B., Wolff, M., Miginiac-Maslow, M. and Rohmer, M. Isoprenoid biosynthesis in plant chloroplasts via the MEP pathway: direct thylakoid/ferredoxin-dependent photoreduction of GcpE/IspG. FEBS Lett. 580 (2006) 1547–1552. [PMID: 16480720]
[EC 1.17.7.1 created 2003 as EC 1.17.4.3, transferred 2009 to EC 1.17.7.1, modified 2014]
 
 
EC 2.3.1.70
Deleted entry: CDP-acylglycerol O-arachidonoyltransferase. This enzyme was deleted following a retraction of the evidence upon which the entry had been drafted (Thompson, W. and Zuk, R.T. Acylation of CDP-monoacylglycerol cannot be confirmed. J. Biol. Chem. 258 (1983) 9623. [PMID: 6885763]).
[EC 2.3.1.70 created 1984, deleted 2009]
 
 
*EC 2.5.1.41
Accepted name: phosphoglycerol geranylgeranyltransferase
Reaction: geranylgeranyl diphosphate + sn-glycerol 1-phosphate = diphosphate + 3-(O-geranylgeranyl)-sn-glycerol 1-phosphate
For diagram of archaetidylserine biosynthesis, click here
Glossary: sn-glycerol 1-phosphate = sn-glyceryl phosphate = (S)-2,3-dihydroxypropyl dihydrogen phosphate
Other name(s): glycerol phosphate geranylgeranyltransferase; geranylgeranyl-transferase (ambiguous); prenyltransferase (ambiguous); (S)-3-O-geranylgeranylglyceryl phosphate synthase; (S)-geranylgeranylglyceryl phosphate synthase; GGGP synthase; (S)-GGGP synthase; GGGPS; geranylgeranyl diphosphate:sn-glyceryl phosphate geranylgeranyltransferase; geranylgeranyl diphosphate:sn-glycerol-1-phosphate geranylgeranyltransferase
Systematic name: geranylgeranyl-diphosphate:sn-glycerol-1-phosphate geranylgeranyltransferase
Comments: This cytosolic enzyme catalyses the first pathway-specific step in the biosynthesis of the core membrane diether lipids in archaebacteria [2]. Requires Mg2+ for maximal activity [2]. It catalyses the alkylation of the primary hydroxy group in sn-glycerol 1-phosphate by geranylgeranyl diphosphate (GGPP) in a prenyltransfer reaction where a hydroxy group is the nucleophile in the acceptor substrate [2]. The other enzymes involved in the biosynthesis of polar lipids in Archaea are EC 1.1.1.261 (sn-glycerol-1-phosphate dehydrogenase), EC 2.5.1.42 (geranylgeranylglycerol-phosphate geranylgeranyltransferase) and EC 2.7.7.67 (CDP-archaeol synthase), which lead to the formation of CDP-unsaturated archaeol. The final step in the pathway involves the addition of L-serine, with concomitant removal of CMP, leading to the production of unsaturated archaetidylserine [5].
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, CAS registry number: 124650-69-7
References:
1.  Zhang, D.-L., Daniels, L. and Poulter, C.D. Biosynthesis of archaebacterial membranes. Formation of isoprene ethers by a prenyl transfer reaction. J. Am. Chem. Soc. 112 (1990) 1264–1265.
2.  Chen, A., Zhang, D. and Poulter, C.D. (S)-Geranylgeranylglyceryl phosphate synthase. Purification and characterization of the first pathway-specific enzyme in archaebacterial membrane lipid biosynthesis. J. Biol. Chem. 268 (1993) 21701–21705. [PMID: 8408023]
3.  Nemoto, N., Oshima, T. and Yamagishi, A. Purification and characterization of geranylgeranylglyceryl phosphate synthase from a thermoacidophilic archaeon, Thermoplasma acidophilum. J. Biochem. 133 (2003) 651–657. [PMID: 12801917]
4.  Payandeh, J., Fujihashi, M., Gillon, W. and Pai, E.F. The crystal structure of (S)-3-O-geranylgeranylglyceryl phosphate synthase reveals an ancient fold for an ancient enzyme. J. Biol. Chem. 281 (2006) 6070–6078. [PMID: 16377641]
5.  Morii, H., Nishihara, M. and Koga, Y. CTP:2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate cytidyltransferase in the methanogenic archaeon Methanothermobacter thermoautotrophicus. J. Biol. Chem. 275 (2000) 36568–36574. [PMID: 10960477]
[EC 2.5.1.41 created 1992, modified 2009]
 
 
*EC 2.5.1.42
Accepted name: geranylgeranylglycerol-phosphate geranylgeranyltransferase
Reaction: geranylgeranyl diphosphate + 3-(O-geranylgeranyl)-sn-glycerol 1-phosphate = diphosphate + 2,3-bis-(O-geranylgeranyl)-sn-glycerol 1-phosphate
For diagram of archaetidylserine biosynthesis, click here
Other name(s): geranylgeranyloxyglycerol phosphate geranylgeranyltransferase; geranylgeranyltransferase II; (S)-2,3-di-O-geranylgeranylglyceryl phosphate synthase; DGGGP synthase; DGGGPS; geranylgeranyl diphosphate:sn-3-O-(geranylgeranyl)glycerol 1-phosphate geranylgeranyltransferase
Systematic name: geranylgeranyl diphosphate:3-(O-geranylgeranyl)-sn-glycerol 1-phosphate geranylgeranyltransferase
Comments: This enzyme is an integral-membrane protein that carries out the second prenyltransfer reaction involved in the formation of polar membrane lipids in Archaea. Requires a divalent metal cation, such as Mg2+ or Mn2+, for activity [2]. 4-Hydroxybenzoate, 1,4-dihydroxy 2-naphthoate, homogentisate and α-glycerophosphate cannot act as prenyl-acceptor substrates [2]. The other enzymes involved in the biosynthesis of polar lipids in Archaea are EC 1.1.1.261 (sn-glycerol-1-phosphate dehydrogenase), EC 2.5.1.41 (phosphoglycerol geranylgeranyltransferase), which, together with this enzyme, alkylates the hydroxy groups of glycerol 1-phosphate to yield unsaturated archaetidic acid, which is acted upon by EC 2.7.7.67 (CDP-archaeol synthase) to form CDP-unsaturated archaeol. The final step in the pathway involves the addition of L-serine, with concomitant removal of CMP, leading to the production of unsaturated archaetidylserine [3]. Belongs in the UbiA prenyltransferase family [2].
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, CAS registry number: 124650-68-6
References:
1.  Zhang, D.-L., Daniels, L. and Poulter, C.D. Biosynthesis of archaebacterial membranes. Formation of isoprene ethers by a prenyl transfer reaction. J. Am. Chem. Soc. 112 (1990) 1264–1265.
2.  Hemmi, H., Shibuya, K., Takahashi, Y., Nakayama, T. and Nishino, T. (S)-2,3-Di-O-geranylgeranylglyceryl phosphate synthase from the thermoacidophilic archaeon Sulfolobus solfataricus. Molecular cloning and characterization of a membrane-intrinsic prenyltransferase involved in the biosynthesis of archaeal ether-linked membrane lipids. J. Biol. Chem. 279 (2004) 50197–50203. [PMID: 15356000]
3.  Morii, H., Nishihara, M. and Koga, Y. CTP:2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate cytidyltransferase in the methanogenic archaeon Methanothermobacter thermoautotrophicus. J. Biol. Chem. 275 (2000) 36568–36574. [PMID: 10960477]
[EC 2.5.1.42 created 1992, modified 2009]
 
 
EC 2.7.7.67
Accepted name: CDP-2,3-bis-(O-geranylgeranyl)-sn-glycerol synthase
Reaction: CTP + 2,3-bis-(O-geranylgeranyl)-sn-glycerol 1-phosphate = diphosphate + CDP-2,3-bis-(O-geranylgeranyl)-sn-glycerol
For diagram of archaetidylserine biosynthesis, click here
Glossary: 2,3-bis-(O-geranylgeranyl)-sn-glycerol 1-phosphate = 2,3-bis-(O-geranylgeranyl)-glycerophosphate ether = unsaturated archaetidic acid
CDP-unsaturated archaeol = CDP-2,3-bis-(O-geranylgeranyl)-sn-glycerol
Other name(s): carS (gene name); CDP-2,3-di-O-geranylgeranyl-sn-glycerol synthase; CTP:2,3-GG-GP ether cytidylyltransferase; CTP:2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate cytidyltransferase; CDP-2,3-bis-O-(geranylgeranyl)-sn-glycerol synthase; CTP:2,3-bis-O-(geranylgeranyl)-sn-glycero-1-phosphate cytidylyltransferase; CDP-unsaturated archaeol synthase; CDP-archaeol synthase (incorrect)
Systematic name: CTP:2,3-bis-(O-geranylgeranyl)-sn-glycerol 1-phosphate cytidylyltransferase
Comments: This enzyme catalyses one of the steps in the biosynthesis of polar lipids in archaea, which are characterized by having an sn-glycerol 1-phosphate backbone rather than an sn-glycerol 3-phosphate backbone as is found in bacteria and eukaryotes [1]. The enzyme requires Mg2+ and K+ for maximal activity [1].
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB, CAS registry number: 329791-09-5
References:
1.  Morii, H., Nishihara, M. and Koga, Y. CTP:2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate cytidyltransferase in the methanogenic archaeon Methanothermobacter thermoautotrophicus. J. Biol. Chem. 275 (2000) 36568–36574. [PMID: 10960477]
2.  Morii, H. and Koga, Y. CDP-2,3-di-O-geranylgeranyl-sn-glycerol:L-serine O-archaetidyltransferase (archaetidylserine synthase) in the methanogenic archaeon Methanothermobacter thermautotrophicus. J. Bacteriol. 185 (2003) 1181–1189. [PMID: 12562787]
3.  Jain, S., Caforio, A., Fodran, P., Lolkema, J.S., Minnaard, A.J. and Driessen, A.J. Identification of CDP-archaeol synthase, a missing link of ether lipid biosynthesis in Archaea. Chem. Biol. 21 (2014) 1392–1401. [PMID: 25219966]
[EC 2.7.7.67 created 2009, modified 2014]
 
 
EC 4.2.1.114
Accepted name: methanogen homoaconitase
Reaction: (R)-2-hydroxybutane-1,2,4-tricarboxylate = (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate (overall reaction)
(1a) (R)-2-hydroxybutane-1,2,4-tricarboxylate = (Z)-but-1-ene-1,2,4-tricarboxylate + H2O
(1b) (Z)-but-1-ene-1,2,4-tricarboxylate + H2O = (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate
For diagram of the 2-aminoadipate pathway of L-lysine synthesis, click here
Glossary: cis-homoaconitate = (Z)-but-1-ene-1,2,4-tricarboxylate
(R)-homocitrate = (R)-2-hydroxybutane-1,2,4-tricarboxylate
homoisocitrate = (-)-threo-homoisocitrate = (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate
Other name(s): methanogen HACN
Systematic name: (R)-2-hydroxybutane-1,2,4-tricarboxylate hydro-lyase [(1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate-forming]
Comments: This enzyme catalyses several reactions in the pathway of coenzyme-B biosynthesis in methanogenic archaea. Requires a [4Fe-4S] cluster for activity. In contrast to EC 4.2.1.36, homoaconitate hydratase, this enzyme can catalyse both the dehydration of (R)-homocitrate to form cis-homoaconitate and the subsequent hydration reaction that forms homoisocitrate. In addition to cis-homoaconitate, the enzyme can also catalyse the hydration of the physiological substrates dihomocitrate and trihomocitrate as well as the non-physiological substrate tetrahomocitrate. cis-Aconitate and threo-DL-isocitrate cannot act as substrates, and (S)-homocitrate and trans-homoaconitate act as inhibitors of the enzyme.
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB
References:
1.  Drevland, R.M., Jia, Y., Palmer, D.R. and Graham, D.E. Methanogen homoaconitase catalyzes both hydrolyase reactions in coenzyme B biosynthesis. J. Biol. Chem. 283 (2008) 28888–28896. [PMID: 18765671]
[EC 4.2.1.114 created 2009]
 
 
EC 4.2.1.115
Accepted name: UDP-N-acetylglucosamine 4,6-dehydratase (configuration-inverting)
Reaction: UDP-N-acetyl-α-D-glucosamine = UDP-2-acetamido-2,6-dideoxy-β-L-arabino-hex-4-ulose + H2O
For diagram of UDP-N-acetyl-β-L-fucosamine biosynthesis, click here and for diagram of mechanism, click here
Glossary: pseudaminic acid = 5,7-bis(acetylamino)-3,5,7,9-tetradeoxy-L-glycero-α-L-manno-2-nonulopyranosonic acid
Other name(s): FlaA1; UDP-N-acetylglucosamine 5-inverting 4,6-dehydratase; PseB; UDP-N-acetylglucosamine hydro-lyase (inverting; UDP-2-acetamido-2,6-dideoxy-β-L-arabino-hex-4-ulose-forming)
Systematic name: UDP-N-acetyl-α-D-glucosamine hydro-lyase (inverting; UDP-2-acetamido-2,6-dideoxy-β-L-arabino-hex-4-ulose-forming)
Comments: Contains NADP+ as a cofactor. This is the first enzyme in the biosynthetic pathway of pseudaminic acid [3], a sialic-acid-like sugar that is unique to bacteria and is used by Helicobacter pylori to modify its flagellin. This enzyme plays a critical role in H. pylori’s pathogenesis, being involved in the synthesis of both functional flagella and lipopolysaccharides [1,2]. It is completely inhibited by UDP-α-D-galactose. The reaction results in the chirality of the C-5 atom being inverted. It is thought that Lys-133 acts sequentially as a catalytic acid, protonating the C-6 hydroxy group and as a catalytic base, abstracting the C-5 proton, resulting in the elimination of water. This enzyme belongs to the short-chain dehydrogenase/reductase family of enzymes.
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB
References:
1.  Ishiyama, N., Creuzenet, C., Miller, W.L., Demendi, M., Anderson, E.M., Harauz, G., Lam, J.S. and Berghuis, A.M. Structural studies of FlaA1 from Helicobacter pylori reveal the mechanism for inverting 4,6-dehydratase activity. J. Biol. Chem. 281 (2006) 24489–24495. [PMID: 16651261]
2.  Schirm, M., Soo, E.C., Aubry, A.J., Austin, J., Thibault, P. and Logan, S.M. Structural, genetic and functional characterization of the flagellin glycosylation process in Helicobacter pylori. Mol. Microbiol. 48 (2003) 1579–1592. [PMID: 12791140]
3.  Schoenhofen, I.C., McNally, D.J., Brisson, J.R. and Logan, S.M. Elucidation of the CMP-pseudaminic acid pathway in Helicobacter pylori: synthesis from UDP-N-acetylglucosamine by a single enzymatic reaction. Glycobiology 16 (2006) 8C–14C. [PMID: 16751642]
[EC 4.2.1.115 created 2009]
 
 
EC 4.2.3.38
Accepted name: α-bisabolene synthase
Reaction: (2E,6E)-farnesyl diphosphate = (E)-α-bisabolene + diphosphate
For diagram of bisabolene-derived sesquiterpenoid biosynthesis, click here
Other name(s): bisabolene synthase
Systematic name: (2E,6E)-farnesyl-diphosphate diphosphate-lyase [(E)-α-bisabolene-forming]
Comments: This cytosolic sesquiterpenoid synthase requires a divalent cation cofactor (Mg2+ or, to a lesser extent, Mn2+) to neutralize the negative charge of the diphosphate leaving group. While unlikely to encounter geranyl diphosphate (GDP) in vivo as it is localized to plastids, the enzyme can use GDP as a substrate in vitro to produce (+)-(4R)-limonene [cf. EC 4.2.3.20, (R)-limonene synthase]. The enzyme is induced as part of a defense mechanism in the grand fir Abies grandis as a response to stem wounding.
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB
References:
1.  Bohlmann, J., Crock, J., Jetter, R. and Croteau, R. Terpenoid-based defenses in conifers: cDNA cloning, characterization, and functional expression of wound-inducible (E)-α-bisabolene synthase from grand fir (Abies grandis). Proc. Natl. Acad. Sci. USA 95 (1998) 6756–6761. [PMID: 9618485]
[EC 4.2.3.38 created 2009]
 
 
EC 4.2.3.39
Accepted name: epi-cedrol synthase
Reaction: (2E,6E)-farnesyl diphosphate + H2O = 8-epi-cedrol + diphosphate
For diagram of bisabolene-derived sesquiterpenoid biosynthesis, click here
Other name(s): 8-epicedrol synthase; epicedrol synthase
Systematic name: (2E,6E)-farnesyl-diphosphate diphosphate-lyase (8-epi-cedrol-forming)
Comments: The enzyme is activated by Mg2+ [2]. Similar to many other plant terpenoid synthases, this enzyme produces many products from a single substrate. The predominant product is the cyclic sesquiterpenoid alcohol, 8-epi-cedrol, with minor products including cedrol and the olefins α-cedrene, β-cedrene, (E)-β-farnesene and (E)-α-bisabolene [1].
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB
References:
1.  Mercke, P., Crock, J., Croteau, R. and Brodelius, P.E. Cloning, expression, and characterization of epi-cedrol synthase, a sesquiterpene cyclase from Artemisia annua L. Arch. Biochem. Biophys. 369 (1999) 213–222. [PMID: 10486140]
2.  Hua, L. and Matsuda, S.P. The molecular cloning of 8-epicedrol synthase from Artemisia annua. Arch. Biochem. Biophys. 369 (1999) 208–212. [PMID: 10486139]
[EC 4.2.3.39 created 2009]
 
 
EC 4.2.3.40
Accepted name: (Z)-γ-bisabolene synthase
Reaction: (2E,6E)-farnesyl diphosphate = (Z)-γ-bisabolene + diphosphate
For diagram of bisabolene-derived sesquiterpenoid biosynthesis, click here
Systematic name: (2E,6E)-farnesyl-diphosphate diphosphate-lyase [(Z)-γ-bisabolene-forming]
Comments: This sesquiterpenoid enzyme is constitutively expressed in the root, hydathodes and stigma of the plant Arabidopsis thaliana. If the leaves of the plant are wounded, e.g. by cutting, the enzyme is also induced close to the wound site. The sesquiterpenoids (E)-nerolidol and α-bisabolol are also produced by this enzyme as minor products.
Links to other databases: BRENDA, EXPASY, IUBMB, KEGG, PDB
References:
1.  Ro, D.K., Ehlting, J., Keeling, C.I., Lin, R., Mattheus, N. and Bohlmann, J. Microarray expression profiling and functional characterization of AtTPS genes: duplicated Arabidopsis thaliana sesquiterpene synthase genes At4g13280 and At4g13300 encode root-specific and wound-inducible (Z)-γ-bisabolene synthases. Arch. Biochem. Biophys. 448 (2006) 104–116. [PMID: 16297850]
[EC 4.2.3.40 created 2009]
 
 


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