Involved in the degradation of 4-sulfocatechol which is a central intermediate in the degradation of substituted sulfonated benzenes. Catalyzes the hydrolytical desulfonation of 4-sulfomuconolactone to yield maleylacetate. 4-sulfomuconolactone + H2O = 2 H(+) + maleylacetate + sulfite Completely inhibited by ZnCl(2) and CuCl(2). kcat is 2700 min(-1) with 4-sulfomuconolactone (at pH 8). Optimum pH is between 7 and 7.5. Approximately 30% of the maximal activities are still detected at pH 5 and pH 9. Monomer. Belongs to the metallo-dependent hydrolases superfamily. Sulfomuconolactone hydrolase family.