IUBMB Enzyme Nomenclature


Accepted name: methanogen homoaconitase

Reaction: (R)-2-hydroxybutane-1,2,4-tricarboxylate + H2O = (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

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, 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 dihomoaconitate and trihomoaconitate as well as the non-physiological substrate tetrahomoaconitate. 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, KEGG, Metacyc, PDB, CAS registry number:


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 created 2009]

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