Page 215 - The Toxicology of Fishes

Biotransformation in Fishes 195

Exposure to metals, pyrollizidine alkaloids, pesticides,
peroxidized oils, toxic algae, fatty diet

Generation of reactive oxygen species
(O2 , H2O2, HO ) •
•—

Lipid peroxidation
Liver
Protein and DNA disease,
Release toxic α, β damage mortality
unsaturated aldehydes
4 hydroxynonenal, 4HNE
H GST,
ADH Detoxification
O
O ALDH
FIGURE 4.13 Pathway for the generation and detoxification of 4-hydroxynonenal (4HNE). In mammals and certain fish
species, GST constitutes a protective pathway against 4HNE injury.

the prototypical xenobiotic substrates, with ETHA being the highest. GSTA1 has a fivefold higher
peroxidase activity (25 µmol/min/mg protein). The purified GSTA homolog of sea bass displays the same
characteristic profile of a high activity with N2E and relatively high activity with ETHA compared with
other substrates.
Largemouth bass (Micropterus salmoides) expresses a liver GST that shares extensive sequence
identity to the aforementioned 4HNE-metabolizing GSTA isolated from plaice that detoxifies 4HNE.
Interestingly, the bass GST exhibits a catalytic activity toward 4HNE that exceeds that of several
mammalian and aquatic species (Doi et al., 2004; Pham et al., 2002). Bass GSTA is also similar to a
GST form found in two other fish species (European flounder and fathead minnow); however, similar
genes may not be present in other aquatic species. Bass GSTA exhibits little sequence identity (21% or

TABLE 4.14
The Catalytic Properties of Glutathione S-Transferase in Cytosol and Glutathione Affinity-Column-Purified
Fractions from Several Fish Species
Activity
(nmol/min/mg protein)
Species Preparation Ref. BPDE EA CDNB

Catfish Liver cytosol Gallagher et al. (1996) 5.3 37 1325
(Ictalurus punctatus) Affinity purified fraction 128 — 24.000
Intestinal cytosol Gadagbui and James 8.3 65 1010
Affinity purified fraction (2000) 453 2880 107,000
Brown bullhead Liver cytosol Henson et al. (2001) <5 — 1130
(Ameiurus nebulosus) Affinity purified fraction 310 — 5,700
Rainbow trout Liver cytosol Melgar Riol et al. (2001) — 20 630
(Oncorhynchus mykiss) Affinity purified fraction — 2030 77,180
Atlantic salmon Liver cytosol Novoa-Valinas et al. (2002) — 70 290
(Salmo salar) Affinity purified fraction — 4350 16,600
Kidney cytosol Novoa-Valinas et al. (2002) — 60 200
Affinity purified fraction — 10,620 37,500
Brown trout Liver cytosol Novoa-Valinas et al. (2002) — 90 650
(Salmo trutta) Affinity purified fraction — 3790 27,690
Note: BPDE, (+)-anti-benzo(a)pyrene-7,8-dihydrodiol-9,10-oxide; EA, ethacrynic acid; CDNB, 1-chloro-2,4-dini-
trobenzene.