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Two groups of sulfotransferease (SULT) enzymes catalyze the transfer of a sulfate group from 3-phosphoadenosine 5-phosphosulfate (PAPS) to a hydroxyl group on an acceptor molecule, yielding a sulfonated acceptor and 3-phosphoadenosine 5-phosphate (PAP). One is localized to the Golgi apparatus and mediates the sulfonation of proteoglycans. The second, annotated here, is cytosolic and mediates the sulfonation of a diverse array of small molecules, increasing their solubilities in water and modifying their physiological functions. There are probably thirteen or more human cytosolic SULT enzymes; eleven of these have been purified and characterized enzymatically, and are annotated here (Blanchard et al. 2004; Gamage et al. 2005). These enzymes appear to be active as dimers. Their substrate specificities are typically broad, and not related in an obvious way to their structures; indeed, apparently orthologous human and rodent SULT enzymes can have different substrate specificities (Glatt 2000), and none has been exhaustively characterized. The substrates listed in the table and annotated here are a sample of the known ones, chosen to indicate the range of activity of these enzymes and to capture some of their known physiologically important targets. Absence of a small molecule - enzyme pair from the table, however, may only mean that it has not yet been studied.
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