using a procedure described previously (James et al., 1997). Only the proximal portion of

the intestine was used in the study. Protein determination was carried out by the method

of Lowry and co-workers (195 1) using bovine serum albumin as protein standard.

 Glucuronidation assay. A radiochemical ion-pair extraction method was

employed to investigate the glucuronidation of the 4-OHPCBs and 4-OHBP. Substrate

consumption did not exceed 10%. Initial experiments determined the saturating

concentrations of UDPGA to be employed. The incubation mixture consisted of 0.1 M

Tris-Cl buffer (pH 7.6), 5 mM MgCl2, 0.5% Brij-58, 200 CIM or 1500 CIM [14C]UDPGA

(intestine and liver, respectively), 100 Clg catfish intestinal or hepatic microsomal protein,

and substrate in a total reaction volume of 0. 1 mL. Initially, the OH-PCBs were added to

tubes from methanol solutions and evaporated under nitrogen. In all cases, the protein

and Brij-58 were added to the dried substrate, thoroughly vortexed and left on ice for 30

minutes. Subsequently, the buffer, MgCl2, and water were added in that order and vortex-

mixed. After a pre-incubation of 3 minutes at 35oC, UDPGA was added to initiate the

reaction, which was terminated after 30 minutes incubation by the addition of a 1:1

mixture of 2.5% acetic acid and PIC-A in water, such that the final volume was 0.5 mL.

The glucuronide product was extracted by two successive 1.5 mL portions of ethyl

acetate. The phases were separated by centrifugation, and duplicate portions of the ethyl

acetate phase were counted for quantitation of glucuronide conjugate.

 Physicochemical parameters. The structural characteristics of the OH-PCBs were

calculated using ChemDraw 3D (CambridgeSoft Corp., Cambridge, MA). Parameters

used were: the Connolly Accessible Surface Area (CAA, the locus of the center of a

probe sphere, representing the solvent, as it is rolled over the molecular shape), the