Arylsulfatase B using calcium cofactor (ARSB:Ca2+) hydrolyses sulfate from N-acetylgalactosamine 4-sulfate (or 6-sulfate) units (GalNAc 4-sulfate or GalNAc 6-sulfate) within chondroitin sulfate (Gorham & Cantz 1978). The conversion to 3-oxoalanine (formylglycine, FGly) of a cysteine residue in eukaryotes, is critical for catalytic activity, based on similarity to the prototypical arylsulfatase ARSA (Chruszcz et al. 2003, Lukatela et al. 1998). Defects in ARSB are the cause of mucopolysaccharidosis type VI (MPSVI) (MIM:253200, also called Maroteaux-Lamy syndrome (Wicker et al. 1991). ARSB activity is defective in multiple sulfatase deficiency (MSD) (MIM:272200) (Schmidt et al. 1995).