Catalyzes the isomerization of citrate to isocitrate via cis-aconitate, a step in the citric acid cycle. citrate = D-threo-isocitrate Binds 1 [4Fe-4S] cluster per subunit. Carbohydrate metabolism; tricarboxylic acid cycle; isocitrate from oxaloacetate: step 2/2. Monomer. Belongs to the aconitase/IPM isomerase family.