In enzymology, a 2-chloro-4-carboxymethylenebut-2-en-1,4-olide isomerase is an enzyme that catalyzes the chemical reaction cis-2-chloro-4-carboxymethylenebut-2-en-1,4-olide ⇌ {\displaystyle \rightleftharpoons } trans-2-chloro-4-carboxymethylenebut-2-en-1,4-olideHence, this enzyme has one substrate, cis-2-chloro-4-carboxymethylenebut-2-en-1,4-olide, and one product, trans-2-chloro-4-carboxymethylenebut-2-en-1,4-olide. Wikipedia