While no UGTs have yet been cloned and characterized from channel catfish, this

species shows glucuronidation activity towards a variety of toxic xenobiotics, including

mono- and di-hydroxy metabolites of benzo[a]pyrene and OH-PCBs (James et al., 2001;

van den Hurk and James 2001; Gaworecki et al., 2004). As with other aquatic species,

pollutants which are direct substrates for glucuronidation, such as pentachlorophenol,

several OH-PCBs, 4-OH-heptachlorostyrene, and which have been shown to be

estrogenic and thyroidogenic, have been detected in channel catfish (Li et al., 2003).

Kinetic differences have been observed between hepatic and intestinal UGT activities,

suggesting expression of different isozymes in these two organs. Thus, knowing more

about the identity and substrate specificity of catfish UGTs will assist our understanding

of the effect of glucuronidation on the contributions of such metabolites to toxicity. Since

the absence of cDNAs with the same 3'sequence and dissimilar 5'exon 1 coding

sequence in fish suggests the absence of alternative splicing of UGTIA genes as seen in

mammals (Gong et al., 2001), additional information on piscine UGT gene structure is

also important from a phylogenetic perspective.

 Hypothesis

 Multiple UGT isoforms are present in channel catfish liver and intestine

 Methodology (part 1)

 For convenience, a flowchart summarizing the various steps involved in the cloning

process is shown in Figure 5-1. Because the study utilizing the gene specific primers was

dependent on an initial study which utilized degenerate primers and led to the cloning of

partial sequences of UGT, the methodology and results sections are split correspondingly

mn two parts.