Enzyme with broad specificity that catalyzes reversible hydroxyacid isomerizations via dehydration/hydration reactions. Catalyzes the isomerization between 2-isopropylmalate and 3-isopropylmalate, via the formation of 2-isopropylmaleate, a step involved in leucine biosynthesis. Catalyzes the isomerization between 2-methylmalate and 3-methylmalate, via the formation of 2-methylmaleate (citraconate), a step involved in isoleucine biosynthesis. Also displays malease activity, i.e. catalyzes the hydration of maleate to form (R)-malate. (2R,3S)-3-isopropylmalate = (2S)-2-isopropylmalate (3R)-citramalate = 2-methylmaleate + H2O 2-methylmaleate + H2O = (2R,3S)-3-methylmalate (R)-malate = H2O + maleate Binds 1 [4Fe-4S] cluster per subunit. Optimum pH is 7.5. Optimum temperature is 70 degrees Celsius. Amino-acid biosynthesis; L-leucine biosynthesis; L-leucine from 3-methyl-2-oxobutanoate: step 2/4. Amino-acid biosynthesis; L-isoleucine biosynthesis; 2-oxobutanoate from pyruvate: step 2/3. Heterotetramer of 2 LeuC and 2 LeuD. Cannot form a complex with HacB. Belongs to the aconitase/IPM isomerase family. LeuC type 2 subfamily.