3'-Phosphoadenosine-5'-Phosphosulfate

Inorganic sulfur in the environment (sulfate, sulfur, or sulfite) must undergo fixation to be ulitized by organisms. The process for sulfate is largely confined to plants and bacteria. Activation of sulfur for reduction is in the form of the intermediate called PAPS (3'-phosphoadenosine-5'-phosphosulfate) (see here). PAPS is formed in a two-step reaction (see here).

See here: Metabolism of Sulfur-Containing Amino Acids