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Parent Class:

EC-Numbers → 4 -- Lyases → 4.2 -- Carbon-oxygen lyases → 4.2.1 -- Hydro-lyases

Synonyms: homoaconitase, cis-homoaconitase, HACN, Lys⁴, LysF, 2-hydroxybutane-1,2,4-tricarboxylate hydro-lyase (incorrect)

Systematic Name: (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate hydro-lyase [(Z)-but-1-ene-1,2,4-tricarboxylate-forming]

Unification Links: BRENDA:4.2.1.36, ENZYME:4.2.1.36, IUBMB-ExplorEnz:4.2.1.36

Reaction:
(1R,2S)-homoisocitrate ← cis-homoaconitate + H₂O

Enzymes and Genes:
methanogen homoaconitase: hacB, hacA ( Methanocaldococcus jannaschii )
homoaconitase: lysU, lysT ( Thermus thermophilus )
homoaconitase: LYS4 ( Saccharomyces cerevisiae )

Summary:
Requires a [4Fe-4S] cluster for activity. The enzyme from the hyperthermophilic eubacterium Thermus thermophilus can catalyse the reaction shown above but cannot catalyse the previously described reaction, i.e. formation of (R)-homocitrate by hydration of cis-homoaconitate. The enzyme responsible for the conversion of cis-homoaconitate into (R)-homocitrate in T. thermophilus is unknown at present but the reaction can be catalysed in vitro using aconitate hydratase from pig ( EC 4.2.1.3) [2].

Citations: [Strassman66, Zabriskie00, Jia06]