SULT1A3 and SULT1B1 did not exhibit substrate inhibition over a concentration range up to 5 [micro]M and showed much higher apparent [K.sub.m] values for 3-OH-BaP.
As shown in Figure 7, expressed SULT1A3 was not inhibited or was weakly inhibited by OH-PCBs when 3-OH-BaP was used at the noninhibitory concentration of 1.0 [micro]M.
Expressed SULT1B1 showed a quite different inhibitory interaction with OH-PCBs, compared with SULT1A1*1, SULT1A1*2, SULT1A3, and SULTIE1, in that 6'-OHCB35 (A1) was a quite potent inhibitor (I[C.sub.50], 4.72 [micro]M) of 3-OH-BaP sulfonation (Table 3).
A related compound, 1-hydroxypyrene, also had a very low [K.sub.m] with SULT1A1 (8 nM) and SULT1E1 (21 nM) but a higher [K.sub.m] with SULT1A3 (0.8 [micro]M) (Ma et al.