Sulfur is an essential element in all lifeforms used in the synthesis of sulfur-containing amino acids, maintenance of cellular redox states and detoxifying toxic compounds. 3'-phosphoadenosine 5'-phosphosulfate (PAPS) is the active form of sulfur used in these reactions, which consume PAPS, producing 3'-phosphoadenosine 5'-phosphate (PAP). PAP is degraded to 5′-AMP (AMP) by 3′-nucleotidase family. Mammals encode two 3′-nucleotidases, the Golgi-resident inositol monophosphatase 3 (IMPAD3 aka PAP phosphatase, gPAPP) and the cytosolic bisphosphate 3′-nucleotidase 1 (BPNT1, described in its own reaction). Both require Mg2+ as cofactor and both are inhibited by lithium (Hudson et al. 2013).