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Abstract

The sulfation reaction catalyzed by the cytosolic sulfotransferases (STs) plays a role in the biological function of numerous endogenous compounds. The list includes steroids, bile acids, iodothyronines, catecholamines, and other bioactive amines, such as 5-hydroxytryptamine. This function must be considered along with the role of sulfation in the detoxication of xenobiotics and in steroid hormone biosynthesis. The sulfation system comprises ST enzymes, the arylsulfatases, which are capable of hydrolyzing the sulfate conjugates of many compounds; the bifunctional sulfate activating enzyme (ATP sulfurylase-APS kinase), which synthesizes the sulfation reaction cosubstrate PAPS (3’ phosphoadenosine 5’-phosphosulfate) from ATP and inorganic sulfate; and the transport mechanisms, which import and export the polar sulfate conjugates into and out of cells. It is clear that genetically and/or environmentally determined levels of each critically shape an individual's overall sulfation capacity. A number of isoforms, all coded by distinct but related genes have been purified and their cDNAs and genes cloned and sequenced. On the basis of the similarity of their derived amino acid sequences and their substrate preferences, these different forms of ST can be classified into one of two subfamilies. There is a single hydroxysteroid sulfotransferase (HST), which will accept numerous steroids (including dehydroepiandrosterone, testosterone, pregnenolone, and cortisol), bile acids, cholesterol, and xenobiotic alcohols. The other sub-family, called phenolsulfotransferase (PST) comprises three closely related enzymes often called P-PST. The human ST principally responsible for the conjugation of catecholamines and other bioactive amines is M-PST. M-PST is expressed at low levels in human liver, whereas expression appears highest in the small intestine. The high level of expression in the small intestinal mucosa may indicate an evolutionary role in detoxication of dietary xenobiotics, in addition to any function it may have in supplying conjugated catecholamines for transport to other tissues. Certain dietary chemicals are known to be substrates for this enzyme.