Resuspension buffer consisted of 0.25 M sucrose, 0.01 M Hepes pH 7.4, 5% glycerol, 0. 1

mM dithiothreitol, 0.1 mM ethylene diamine tetra-acetic acid and 0.1 mM phenylmethyl

sulfonyl fluoride. The liver was placed in a volume of fresh ice-cold buffer equal to 4

times the weight of the liver sample. The cytosol and microsomal fractions were obtained

using a procedure described previously (Wang et al., 2004). Microsomal and cytosolic

protein contents were measured by the Lowry assay, using bovine serum albumin (BSA)

as standard.

Sulfotransferase Assays

A. Fluorometric method. The activity was measured on the basis that at alkaline pH, the

benzo[a]pyrene-3 -O-sulfate has different wavelength optima for fluorescence excitation

and emission (294/415 nm) from the benzo[a]pyrene-3 -O-phenolate anion (3 90/545 nm)

(James et al., 1997). Saturating concentrations of PAPS were determined by performing

the assay at 1 C1M 3-OH-B[a]P. The reaction mixture for detecting the sulfation of 3-OH-

BaP by polar bear liver cytosol consisted of 0.1 M Tris-Cl buffer (pH 7.6), 0.4% BSA,

PAPS (0.02 mM), 25 Clg polar bear hepatic cytosolic protein, and 3-OH-B[a]P (0.05-25

CIM) in a total reaction volume of 1.0 mL. SULT activity (pmol/min/mg) was calculated

from a standard curve prepared with B[a]P-3-O-sulfate standards. Substrate consumption

did not exceed 10%.

B. Radiochemical extraction method. This method, based on Wang and co-workers

(2004), was employed in the study of the sulfonation of 4'-OH-PCB79, 4'-OH-PCBl159,

4'-OH-PCBl65, triclosan, PCP, TCPM and OHMXC. Cytosolic protein concentrations

and incubation time were optimized for every test substrate to ensure that the reaction

was linear during the incubation period. Substrate consumption did not exceed 5%. The