Methanogen homoaconitase (EC 4.2.1.114, methanogen HACN) is an enzyme with systematic name (R)-2-hydroxybutane-1,2,4-tricarboxylate hydro-lyase ((1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate-forming).^[1] This enzyme catalyses the following chemical reaction

(R)-2-hydroxybutane-1,2,4-tricarboxylate ${\displaystyle \rightleftharpoons }$ (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate (overall reaction)

(1a) (R)-2-hydroxybutane-1,2,4-tricarboxylate ${\displaystyle \rightleftharpoons }$ (Z)-but-1-ene-1,2,4-tricarboxylate + H₂O

(1b) (Z)-but-1-ene-1,2,4-tricarboxylate + H₂O ${\displaystyle \rightleftharpoons }$ (1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate

This enzyme catalyses several reactions in the pathway of coenzyme-B biosynthesis in methanogenic archaea.