Table 5-14. Conserved consecutive residues observed in catfish liver and mammalian
 UGTs (sequences shown in Figure 5-13). Xindicates unconserved residue

Residue
Start Sequence Importance Reference

32 GSHWLSM Contains His which is critical for Battaglia et al., 1994
 activity
49 RGH Conserved hydrophobic region; Battaglia et al., 1994
 His required for optimal enzyme Senay et al., 1997
 activity but not involved in catalysis
54 VVLVP Important for enzyme function Senay et al., 1997
144 LTDPF Unknown
199 MTFXQRVKNXL Contains a phosphokinase site (T) Basu et al., 2005
249 WLXRXDF Unknown
263 MPNXVIGGINC Pro and GIy im ortant for UGTIAl Ciotti et al., 1995
 activity and secondary structure
299 VFS/TLGSXVSEI/LP Unknown
324 IPQXVLWRYTG Unknown
424 VL/INNKXYKE Unknown

 A high degree of conservation (77%) was present for proline residues between

catfish and the mammalian UGTs. The unique structure of this cyclic amino acid permits

twists and kinks in the protein's tertiary structure. This indicates that overall, the three-

dimensional structure of catfish liver UGTs is similar to its mammalian homologs.

 On the other hand, there were some important differences. The Ile211 TOSidue which

is essential for activity in human UGTIA10 (Martineau et al., 2004), was replaced by a

Leu in channel catfish (as in human UGTIA1, UGTIA3, UGTIA4, UGTIA6). The

phenylalanine residues at positions 90 and 93 which have shown to be important for the

catalytic activity of UGTIA10 towards phenols such as para-nitrophenol and 4-

methylumbelliferone (Xiong et al., 2006), were absent in the catfish sequence as well as

other fish sequences (Figure 5-22). Further upstream, the strongly conserved binding

motif Y73/72XXTKXYPVP that has been shown to be involved in the binding of phenols in