Esterase D, also known as formylglutathione hydrolase, belongs to the esterase D family. Esterase D is active toward numerous substrates including O-acetylated sialic acids, and it may be involved in the recycling of sialic acids. This protein is used as a genetic marker for retinoblastoma and Wilson's disease. Recombinant Esterase D protein was expressed in E.coli and purified by using conventional chromatography techniques.