3′-Phosphoadenosine-5′-phosphosulfate (PAPS) is a derivative of adenosine monophosphate (AMP) that is phosphorylated at the 3′ position and has a sulfate group attached to the 5′ phosphate.

[1] It is endogenously synthesized by organisms via the phosphorylation of adenosine 5′-phosphosulfate (APS), an intermediary metabolite.

[2] In humans such reaction is performed by bifunctional 3′-phosphoadenosine 5′-phosphosulfate synthases (PAPSS1 and PAPSS2) using ATP as the phosphate donor.

[3][4] APS and PAPS are intermediates in the reduction of sulfate to sulfite, an exothermic conversion that is carried out by sulfate-reducing bacteria.

Reduction of PAPS, a more elaborated sulfate ester, leads also to hydrogen sulfide.