Objective:Polychlorinated biphenyls(PCBs) are a group of persistent pollutants

which are potentially harmful to human health.Hydroxylated PCBs(OH-PCBs) are the biologically active form of PCBs

and there have been reports that OH-PCBs are potent inhibitors of phenol sulfotransferases(SULTs);the present study was to investigate the interactions between OH-PCBs and hydroxysteroid SULTs of human and rat.Methods:Recombinant E.coli strains expressing human hydroxysteroid SULT(SULT2A1) and its rat homologous enzyme SULT2A3 were used as the sources of the expressed enzymes which were then purified to apparently homogeneous proteins;three OH-PCBs were applied to investigate their activities as substrates for the enzymes or inhibitors for the sulfation of other substrates;the enzyme activity was assayed by the formation of 3’

5’-diphosphoadenosine

the reaction product of the co-factor of SULTs.Results:4-OH PCB 34 and 4’-OH PCB 68 were substrates for human SULT2A1;4’-OH PCB 9 did not show substrate activity toward human SULT2A1;however

it inhibited the sulfation of dehydroepiandrosterone(DHEA)and 1-pyrenemethanol catalyzed by this enzyme

and in the mode of competitive inhibition.None of the three OH-PCBs were substrates for rat SULT2A3

nor did they show potent inhibition of the enzyme-catalyzed sulfation of DHEA

a physiologic substrate for the enzyme.Conclusion:There exist significant species differences between human and rat hydroxysteroid SULTs in their specificity and affinity toward OH-PCBs

with human SULT2A1 possessing much more active interactions with OH-PCBs than rat SULT2A3.