Catalyzes the reversible dehydration of (R)-homocitrate to cis-homoaconitate, a step in the alpha-aminoadipate pathway for lysine biosynthesis. (2R)-homocitrate = cis-homoaconitate + H2O Binds 1 [4Fe-4S] cluster per subunit. Amino-acid biosynthesis; L-lysine biosynthesis via AAA pathway; L-alpha-aminoadipate from 2-oxoglutarate: step 2/5. Constitutively expressed with a small induction when both glutamate and lysine are missing. Has very little effect on growth on nonfermentable carbon sources. The fermenting yeast S.cerevisiae has 2 aconitases, ACO1 essential for the citric acid cycle, and ACO2 specifically and exclusively contributing to lysine biosynthesis. In contrast, in respiring filamentous fungi the ACO2 homologs (acoB) seem enzymatically inactive and the ACO1 homolog (acoA) is solely responsible for these functions. Present with 4670 molecules/cell in log phase SD medium. Belongs to the aconitase/IPM isomerase family.