ASK is a water soluble enzyme localysed in ER. No tissue localization is specified to date. Based on all above evidences the possible function of ASK is hydrolysis of sulphur ester bonds. Considering the architecture and hydrophobicity of surface catalytic residues, ASK may be binding to substrates which are larger in size to stroids that binds STS and hydrophobic in nature such as sulfated lipids.
Among the different species, high sequence conservation has been seen and suggests an evolutionary conserved gene family sharing a common ancestor. Serine has been identified in bacteria instead of cysteine with modifying factor AstB. Although cysteine has identified first through evolution with modifying factor SUMF1, it has later been established that serine evolved with AstB, which has been transferred to other bacteria through horizontal transfer.