-!- Sulfatase enzymes are classified as type I, in which the key catalytic residue is 3-oxo-L-alanine, type II, which are non-heme iron-dependent dioxygenases, or type III, whose catalytic domain adopts a metallo-beta-lactamase fold and binds two zinc ions as cofactors. -!- Arylsulfatases are type I enzymes, found in both prokaryotes and eukaryotes, with rather similar specificities. -!- The key catalytic residue 3-oxo-L-alanine initiates the reaction through a nucleophilic attack on the sulfur atom in the substrate. -!- This residue is generated by posttranslational modification of a conserved cysteine or serine residue by EC 1.8.3.7, EC 1.1.98.-, serine-type anaerobic sulfatase-maturating enzyme, or EC 1.8.98.-, cysteine-type anaerobic sulfatase-maturating enzyme.