Sulfation biotransformation reaction

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.

异生物化合物的代谢过程包括Ⅰ相和Ⅱ相的生物转化反应，分别涉及化合物的修饰和结合反应。在Ⅰ相生物转化阶段，化合物通过氧化、还原、水解或其他次要反应进行修饰，从而暴露出可与结合分子发生反应的活性基团。在Ⅱ相中，小分子结合物与Ⅰ相修饰的化合物发生反应，生成水溶性更高的分子，从而更容易被排泄。硫酸化是Ⅱ相生物转化反应的一种，其中硫酸根作为结合分子，在硫酸转移酶的催化下与底物结合。硫酸首先与ATP分子结合，通过具有硫酰基酶域和APS激酶域的双重功能酶PAPSS1和PAPSS2形成3'-磷酸腺苷-5'-磷酸硫酸酯（PAPS）。从PAPS中，硫酸基团通过硫酸转移酶的作用转移到实际的底物上，从而产生硫酸化的底物和缺乏硫酸的PAP。