obsolete cis-4-[2-(3-hydroxy)-thionaphthenyl]-2-oxo-3-butenoate isomerase activity (obsolete GO:0018839)
OBSOLETE. Catalysis of the reaction: cis-4-(2-(3-hydroxy)-thionaphthenyl)-2-oxo-3-butenoate = trans-4-(2-(3-hydroxy)-thionaphthenyl)-2-oxo-3-butenoate.