Catalyzes the isomerization of citrate to isocitrate via cis-aconitate, a step in the citric acid cycle. Also catalyzes the reversible dehydration of (R)-homocitrate to cis-homoaconitate, a step in the alpha-aminoadipate pathway for lysine biosynthesis. citrate = D-threo-isocitrate (2R)-homocitrate = cis-homoaconitate + H2O Binds 1 [4Fe-4S] cluster per subunit. Carbohydrate metabolism; tricarboxylic acid cycle; isocitrate from oxaloacetate: step 2/2. Amino-acid biosynthesis; L-lysine biosynthesis via AAA pathway; L-alpha-aminoadipate from 2-oxoglutarate: step 2/5. Down-regulated under iron limitation conditions. 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. Belongs to the aconitase/IPM isomerase family.