Sulfotransferase
= Sulfotransferase
A <sulfotransferase> is an <enzyme> that catalyses <biochemical sulfation> by transferring a group from a donor to an acceptor. The IUBMB places these activities in EC 2.8.2, within sulfur-group-transferring <transferases>. Many familiar biochemical examples use <PAPS>, with <adenosine 3',5'-bisphosphate> as the donor-derived product.<Enzyme Nomenclature by the IUBMB>[EC 2 Introduction, section 2.8; EC 2.8.2.5, 2.8.2.8 and 2.8.2.17, Reactions]{ref}
The acceptor and the modified atom distinguish particular activities. <Chondroitin 4-sulfotransferase> and <chondroitin 6-sulfotransferase> modify different positions of <N-acetylgalactosamine> in <chondroitin>. <Heparan sulfate glucosamine N-sulfotransferase> instead concerns a nitrogen position in <heparan sulfate>. The shared donor does not make these acceptor reactions identical.<Chondroitin 4-sulfotransferase in IUBMB Enzyme Nomenclature>[EC 2.8.2.5, Comments]{ref}<Chondroitin 6-sulfotransferase in IUBMB Enzyme Nomenclature>[EC 2.8.2.17, Comments]{ref}<Heparan sulfate glucosamine N-sulfotransferase in IUBMB Enzyme Nomenclature>[EC 2.8.2.8, Reaction]{ref}
A constructed assay example shows why an activity label needs a measured product. Suppose two samples each consume ten nanomoles of <PAPS>, but one transfers the group to acceptor A and the other to acceptor B. A donor-consumption measurement can agree while the acceptor products differ. If a third sample consumes donor through a side reaction, donor loss alone would not even establish the intended transfer.
Testing a <sulfotransferase> therefore joins three questions: which donor is consumed, which acceptor changes, and where the new group is attached. A total incorporation signal addresses an amount; identifying the modified position supplies structural information. This distinction makes a broad enzyme class useful without erasing the chemical specificity of its members.