ABSTRACT
STs (EC 2.8.2) are important enzymes that catalyse the sulphation of neurotransmitters, hormones, drugs and chemicals (Mulder and Jakoby, 1990; Falany, 1991; Pacifici and De Santi 1995; Weinshilboum, 1986). Their subcellular localisation is mainly cytosolic, although membrane bound STs have been found to catalyse the sulfation of glycosaminoglycans (Inoue et a l., 1986; Razi and Lindahl, 1995) and tyrosyl residues within proteins (Huttner, 1982; Lin and Roth, 1990; Rens-Domiano and Roth, 1989). However, since most of the research work on the interindividual variability of STs has been performed on the cytosolic forms, the subsequent discussion will deal with these ones. In human tissue, there are several forms of ST and five forms have been characterised for their substrate specificities, thermal stability, inhibitor sensivity and regulation. Three forms are grouped under the expression phenol-STs (Falany, 1991; Pacifici and De Santi 1995; Weinshilboum 1986). Two of these forms are thermostable and their diagnostic substrate is 4-nitrophenol. They are named TS-PST (Campbell et a l., 1987) or form P (Carter et al., 1983), simply phenol ST (Cappiello et al., 1990; Pacifici and De Santi, 1995) or SULT1A1. The third form is thermolabile and its diagnostic substrate is dopamine. It is then referred to as TL-PST (Sundaram et a l., 1989) or form M (Carter et a l., 1983), simply catechol ST as the functional moiety is the catecholic group of dopamine (Cappiello et a l., 1990; Pacifici and De Santi, 1995) or SULT1A3. Furthermore, there is a form of hydroxy steroid ST named dehydroepiandrosterone ST also referred to as DHEA-ST and its diagnostic substrate is dehydroepiandrosterone (Falany et a l., 1989; Falany et al., 1995). This form is believed to catalyse the sulfation of androsterone, pregnolone, testosterone, estrone, lithocholic acid and taurolithocholic acid (Falany, 1991; Falany et al., 1989). Finally, there is a form of estrogen ST also referred to as EST and its diagnostic substrate is estrone (Falany and Falany, 1996) or estradiol (Song et al., 1998) at nanomolar concentrations.
