3-carboxy-cis,cis-muconate cycloisomerase () is an enzyme that catalyzes the chemical reaction
The enzyme has one substrate, 2-(carboxymethyl)-5-oxo-2,5-dihydro-2-furoic acid, which is converted to 3-carboxy-cis,cis-muconic acid.
This enzyme belongs to the family of isomerases, specifically intramolecular lyases. The systematic name of this enzyme class is 2-carboxy-2,5-dihydro-5-oxofuran-2-acetate lyase (decyclizing). Other names in common use include beta-carboxymuconate lactonizing enzyme, and 3-carboxymuconolactone hydrolase. This enzyme participates in benzoate degradation via hydroxylation.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code .