methanogen homoaconitase;
methanogen HACN

Lyases;
Carbon-oxygen lyases;
Hydro-lyases

(R)-2-hydroxybutane-1,2,4-tricarboxylate hydro-lyase [(1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate-forming]

(R)-2-hydroxybutane-1,2,4-tricarboxylate = (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate (overall reaction) [RN:R09720];
(1a) (R)-2-hydroxybutane-1,2,4-tricarboxylate = (Z)-but-1-ene-1,2,4-tricarboxylate + H2O [RN:R03444];
(1b) (Z)-but-1-ene-1,2,4-tricarboxylate + H2O = (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate [RN:R04371]

R03444 R04371 R09720

(R)-2-hydroxybutane-1,2,4-tricarboxylate [CPD:C01251];
(Z)-but-1-ene-1,2,4-tricarboxylate [CPD:C04002];
H2O [CPD:C00001]

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.

1  [PMID:18765671]

Drevland RM, Jia Y, Palmer DR, Graham DE

Methanogen homoaconitase catalyzes both hydrolyase reactions in coenzyme B biosynthesis.

J. Biol. Chem. 283 (2008) 28888-96.