PathwayStep2702 PathwayStep2703 Formation of PAPS Activation of sulfate GENE ONTOLOGYGO:0050428 PAPS (3'-phosphoadenosine-5'-phosphosulfate), which functions as a sulfate donor in the cell, is synthesized from sulfate and two molecules of ATP in a two-step process (Robbins and Lipmann 1958) catalyzed in vertebrates (including humans - Venkatachalam et al. 1998) by a bifunctional enzyme. PAPS synthesis takes place in the cytosol, and it is either consumed there in the sulfonation of a variety of hormones and xenobiotics, or it is transported to the Golgi apparatus and consumed in the synthesis of proteoglycans like chondroitin sulfate. Two isoforms of the human bifunctional enzyme are known, mutations in one of which are associated with defects in proteoglycan biosynthesis (Girard et al. 1998; ul Haque et al. 1998). Pubmed13575436 Pubmed9576487 Pubmed9668121 Pubmed9771708 Reactome Database ID Release 43174362 Reactome, http://www.reactome.org ReactomeREACT_6840 adenylyl sulfate (APS) + ATP => PAPS + ADP Activation of inorganic sulfate forms APS