This subgroup contains pCLME and related proteins, and belongs to the Lyase class I family. Members of this family for the most part catalyze similar beta-elimination reactions in which a C-N or C-O bond is cleaved with the release of fumarate as one of the products. These proteins are active as tetramers. The four active sites of the homotetrameric enzyme are each formed by residues from three different subunits. CMLE catalyzes the cyclization of 3-carboxy-cis,cis-muconate (3CM) to 4-carboxy-muconolactone in the beta-ketoadipate pathway. This pathway is responsible for the catabolism of a variety of aromatic compounds into intermediates of the citric cycle in prokaryotic and eukaryotic micro-organisms.