Sulfation biotransformation reaction (Homo sapiens)

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Metabolism of xenobiotic compounds consists of phase I and a phase II biotransformation reactions, being compound modification and conjugation reactions respectively. In phase I biotransformation, the compound is modificated via oxidation, reduction, hydrolysis, or other minor reactions, to reveal a reactive group to which a conjugation molecule can react to. In phase II, a small conjugation molecule reacts with the phase I modified molecule, producing a much more water-soluble molecule that can be excreted more easily. Sulfation is a phase II biotransformation reaction in which sulfate acts as a conjugation molecule and binds to a substrate via the catalysis of sulfotransferases. Sulfate is first combined with ATP molecules to form PAPS via the dual function enzymes PAPSS1 and PAPSS2 consisting of a sulfurylase domain and an APS kinase domain. From PAPS the sulfate group is transferred to the actual substrate via the action of sulfotransferases, resulting in a sulfated substrate and the sulfate-lacking PAP.