Itaconic acid (methylenesuccinic acid) is produced from cis-aconitate by the enzyme cis-aconitate decarboxylase, encoded by the cadA gene in Aspergillus terreus. Cis-aconitate is a TCA cycle intermediate formed from citrate by aconitase. By diverting flux from cis-aconitate before it can be converted to isocitrate, itaconate accumulates. It is industrially important as a monomer for bioplastics and resins.