Similar to what has been reported for the glucuronidation of OH-PCBs in rats

(Tampal et al., 2002) and simple phenols by human UGTIA6 (Ethell et al., 2002), the

maximal rate of hepatic glucuronidation decreased with increased steric bulk. In the case

of intestinal glucuronidation this relationship was weaker. The enzyme affinity of

intestinal UGTs increased with increasing molecular size, perhaps because the bulkier

molecules tended to be more lipophilic. However, in contrast, the affinity of the liver

UGTs was not affected as much by the molecular size, at least within the restricted size

range offered by the OH-PCBs studied. At this point, no explanation for this discrepancy

between these two tissues is forthcoming.

 Conclusions and Recommendations

 OH-PCBs are glucuronidated with similar efficiency by channel catfish liver and

proximal intestine. There appear to be differences in the UGT isozyme profile in both

organs. The Vmax for both hepatic and intestinal glucuronidation was decreased with the

addition of a second chlorine atom flanking the phenolic group, which is an arrangement

typical of OH-PCBs that persist in organisms. Future research may be directed towards

cloning, sequencing and characterizing these catfish UGTs, in order to have a better

understanding of the specificity of individual UGT isoforms for particular chlorine

substitution patterns in OH-PCBs.