Table 1.

Dissociation constants for OHPCBs with rSULT1A1 that had been pretreated with either GSH or GSSG

OHPCBs	Chemical structure	IC50a (µM)	Kd values for OHPCBs with rSULT1A1 (µM)b
			Without PAP		With 0.27 mM PAP
			GSH	GSSG	GSH	GSSG
4’-OH PCB 9		—c	12 ± 4	7.1 ± 1.3	3.1 ± 1.5	3.3 ± 0.1
4’-OH PCB 12		—c	4.0 ± 0.8e	2.5 ± 0.7e	3.1 ± 0.01	4.6 ± 1.2e
6’-OH PCB 35		—c	65 ± 32	117 ± 36	3.7 ± 0.01e	3.6 ± 1.3e
4’-OH PCB 35		— c	3.6 ± 0.9	1.6 ± 0.4	1.6 ± 0.1	1.7 ± 0.1
4’-OH PCB 6		23d	0.66 ± 0.2	0.50 ± 0.1	0.88 ± 0.03	0.72 ± 0.01
4’-OH PCB 33		26 d	2.0 ± 0.1	2.5 ± 0.4	2.0 ± 0.01	2.4 ± 0.04
4-OH PCB 14		0.27 d	0.26 ± 0.03	0.22 ± 0.02	0.40 ± 0.05f	0.29 ± 0.04f
4’-OH PCB 68		0.85	0.67 ± 0.1	0.53 ± 0.1	0.47 ± 0.02	0.40 ± 0.04
4-OH PCB 34		0.34	0.37 ± 0.01	0.23 ± 0.01e	0.49g	0.54 ± 0.01

^aIC₅₀ values with rSULT1A1 (all cysteines in the thiol form) were determined previously with 2-naphthol as the substrate [7].

^bK_d values were determined utilizing rSULT1A1 that had been pretreated with either 1 mM GSH or 1 mM GSSG as described in section 2.4, and, unless otherwise indicated, data were fit to a one-site saturation equation with correction for non-specific binding of the ANS probe. Values are means and S.E. of two determinations unless otherwise indicated.

^cThis OHPCB is a substrate for rSULT1A1.

^dThis OHPCB is an inhibitor for the enzyme pretreated with GSH, but it is a substrate for rSULT1A1 pretreated with 1 mM GSSG.

^eThe K_d value shown is the first K_d when the data were fit to a two-site equation; the second K_d was over 35 times greater than the first K_d.

^fThree determinations were performed.

^gA single determination was performed.