Table 4-1. Estimated kinetic parameters (mean & S.D.) for the co-substrate UDPGA in
 the glucuronidation of three different OH-PCBs.
Substrate Substrate Vmax (app) Km (app)
 Concentration (CIM) (nmol/min/mg) (CLM)
Liver
4'-OHCB-3 5 500 0.87 & 0.20 697 & 246

4'-OHCB-72 250 0.32 & 0.14 247 & 162

Intestine
4'-OHCB-69 200 0.20 + 0. 11 27 & 14




 The estimated apparent maximal rate of glucuronidation of polychlorinated

biphenylols by channel catfish ranged from 124-784 pmol/min/mg for proximal intestine

and 404-2838 pmol/min/mg for the liver (Table 4-2). The Kms for individual OH-PCBs

tended to be different in the two organs, with a few exceptions (40HCB2, 4'OHCBl65).

Vmax was significantly higher in liver than in intestine. Conversely, the affinity of

intestinal catfish UGTs (Km range: 42-572 C1M) for the OH-PCBs tested was higher than

for liver UGTs (Km range: 111-1643 CIM). These contrasting differences are reflected in

the lack of any difference in the efficiency of glucuronidation in both organs when all the

OH-PCB substrates were considered (Table 4-3). Vmax for OH-PCB glucuronidation in

both organs were strongly correlated with each other (R2=0.74). This relationship did not

exist for Km (R2=0.003).