Sulfation refers to the biochemical process by which an inorganic sulfate forms a biologically active organic sulfate under the catalysis of an enzyme. Elemental sulfur in the form of inorganic sulfates can only be bioavailable after metabolic activation, such as 5'-adenosine-5' phosphosulfate (APS) and 3'-phosphate glands 3'-phosphoadenosine-5'-phosphosulfate (PAPS). The synthesis of PAPS is two-step catalysis of ATP (adenosine triphosphate) sulfatase and APS kinase. The inorganic sulfate reacts with ATP to form APS and pyrophosphate; then, APS reacts with ATP to form PAPS and ADP (adenosine diphosphate). The family of sulfuric acid transferases is responsible for the transfer of activated sulfate groups from PAPS to various biomolecules such as hormones, neurotransmitters, carbohydrates and protein tyrosine. In addition, APS and PAPS are also used to synthesize reducing sulfur metabolites, such as the components of many proteins - methionine and cysteine.