Human ileum phenol sulfotransferase

Biology and function of the reversible sulfation pathway catalysed by human sulfotransferases and sulfatases

Sulfation and sulfate conjugate hydrolysis play an important role in metabolism, and are catalysed by members of the sulfotransferase and sulfatase enzyme super-families. In general, sulfation is a deactivating, detoxication pathway, but for some chemicals the sulfate conjugates are much more reactive than the parent compound. The range of compounds which are sulfated is enormous, yet we still understand relatively little of the function of this pathway. This review summarises current knowledge of the sulfation system and the enzymes involved, and illustrates how heterologous expression of sulfotransferases (SULTs) and sulfatases is aiding our appreciation of the properties of these important proteins. The role of sulfation in the bioactivation of procarcinogens and promutagens is discussed, and new data on the inhibition of the sulfotransferase(s) involved by common dietary components such as tea and coffee are presented. The genetic and environmental factors which are known to influence the activity and expression of human SULTs and sulfatases are also reviewed.

Substrate specificity and some properties of phenol sulfotransferase from human intestinal Caco-2 cells

The phase II metabolic reactions, sulfation and glucuronidation, were studied in a human colon carcinoma cell line (Caco-2), which has been developed as a model of intestinal enterocytes. Phenol sulfotransferase (PST, EC 2.4.2.1) was isolated from Caco-2 cells cultured for 7, 14 and 21 days. The enzyme catalyzed the sulfation of both p-nitrophenol and catecholamines (e.g., dopamine) as well as most catecholamine metabolites. The affinity (Km) of PST for dopamine was much higher than for p-nitrophenol, and the specific activity of PST with both substrates increased with the age of the cells. The thermal stability of Caco-2 PST increased with cell age and was not dependent on the acceptor substrate used. The thermolabile PST from 7-day old cells was more sensitive to NEM than was the thermostable enzyme from 21-day old cells. No UDP-glucuronyltransferase (EC 2.4.1.17) activity was detected in 7-, 14- and 21-day old Caco-2 cells with any of the methods used.

Sulfation in male reproductive organs. Bull and boar testis phenol sulfotransferases

Phenol sulfotransferases (PST) from bull and boar testis were partially purified and characterized. A single form of PST adsorbed on DEAE-cellulose was found in the bull testis, whereas from boar testis two different peaks of PST activity were separated. The bull testis PST and both boar testis enzymes were active with p-nitrophenol and adrenalin. They all showed higher affinity to pNP than to adrenalin and were inhibited by these substrates at higher concentrations. Their optimal pH was at 8.5. Bull testis PST and boar PST II which were adsorbed on DEAE-cellulose were thermostable, whereas boar PST I was thermolabile. Those three PST forms differed in sensitivity to 2,6-dichloro-4-nitrophenol (DCNP), N-ethyl maleimide (NEM), iodoacetamide (IAA) and phenylglyoxal (PG). Bull and boar PST II were more rapidly inactivated in the presence of DCNP than boar PST I. In the presence of NEM, the--SH groups reagent, the bull phenol sulfotransferase and boar PST I lost their activity, whereas the activity of boar PST increased. Also iodoacetamide, another--SH group modificator, raised boar PST II activity and decreased boar PST I activity. DTT, which protects thiol groups, had an opposite effect on the enzymes studied than NEM. Phenylglyoxal, a reagent specific for arginine residues inhibited bull testis PST and both boar phenol sulfotransferases. Substrate protection experiments were also performed to determine the localization of reactive groups in bull and boar testis phenol sulfotransferases.