(2R,3S)-2,3-dimethylmalate = dimethylmaleate + H2O Binds 1 [4Fe-4S] cluster per subunit. Highly active between pH 6.5 and 9.0. Retains 50% and 10% of maximum activity at pH 5.0 and 4.5, respectively. Cofactor degradation; nicotinate degradation; propanoate and pyruvate from 6-hydroxynicotinate: step 7/8. Heterodimer of a large and a small subunit. By nicotinic acid. Belongs to the aconitase/IPM isomerase family. LeuC type 2 subfamily.