Page 322 - The Toxicology of Fishes

302 The Toxicology of Fishes

TABLE 6.3
Representative List of Some of the Antioxidant Enzymes Identified and Partially Characterized in
Studies with Fish
Characterization of
Antioxidant Gene Product Gene Refs.
Gene sequence (full or partial) GPX1 and GPX4 Kryukov and Gladyshev (2000)
Catalase Gerhard et al. (2000)
MT Kille et al. (1992); Schlenk et al. (1996);
Scudiero et al. (2001); Yan and Chan (2002)
QR1 Kobayashi et al. (2002)
GCLC Kobayashi et al. (2002)
GR GenBank
CuZnSOD GenBank
Thioredoxin peroxidase GenBank
Heme oxygenase GenBank
Antibody reactivity or protein MnSOD Orbea et al. (2000); Meyer et al. (2003)
characterization GPx Nagai et al. (2002); Orbea et al. (2000)
Heme oxygenase Schlenk et al. (1996)
Catalase Braunbeck et al. (1991); Orbea et al. (2000)
CuZnSOD Nakano et al. (1995); Capo et al. (1997);
Orbea et al. (2000); Meyer et al. (2003)
MT Van den Hurk et al. (2000)

Enzyme activity QR1 Hasspieler and Di Giulio (1992)
GR Gallagher and Di Giulio (1992)
GCL Gallagher and Di Giulio (1992)
GPx Gallagher and Di Giulio (1992); Nagai et al. (2002)
Glutathione transpeptidase Wallace (1989); Gallagher and Di Giulio (1992)
CuZnSOD Matkovics et al. (1977); Capo et al. (1997)
Catalase Matkovics et al. (1977); Förlin et al. (1995);
Dorval and Hontela (2003)
Note: Sequences submitted to GenBank but not yet published in the literature are included only when no sequence
has been published but are in some cases also available in other species for genes whose sequences have
been published. Genes not traditionally considered antioxidant but that may play a certain antioxidant role
(e.g., GSTs or UDPGTs, as discussed in the text) are not included in this table.

enzymes. As a result, the number of enzymes performing specific catalytic activities, their molecular
regulation, and their biochemical characteristics are usually unknown. Studies that have been carried
out with genes related to xenobiotic metabolism such as the UGTs (Clarke et al., 1992; George and
Taylor, 2002), GSTs (Gadagbui and James, 2000; Leaver et al., 1997; Ramage and Nimmo, 1984), and
AhR pathways (Hahn, 2002), as well as other gene families such as the Hox genes (McClintock et al.,
2001) in fish, suggest that multiple isoenzymes will be discovered in many fish species, perhaps in some
cases more than observed in mammals. Some evidence already exists supporting the possibility of
multiple antioxidant isoenzymes such as glutathione peroxidases (Kryukov and Gladyshev, 2000) and
metallothioneins (Bargelloni et al., 1999) in fish. Unique catalytic properties that may belong to novel
enzymes have been identified in fish species (Hasspieler and Di Giulio, 1994). A theoretical reason to
expect multiple antioxidant enzymes in fish is that many fish species are tetraploid because of a
chromosome duplication event that occurred after the phylogenetic divergence of ray-finned fishes from
other vertebrates (Carroll, 1988). Furthermore, in addition to differences between mammals and fishes,
it is likely that very large differences will be identified among different fish species, given the long time
over which fish species have been evolving.