152
V. Carginale et al.
support a metal storage function of MT, which may acquire a particular
relevance at specific stages of organism life, such as embryonic
development and growth [15]. This does 1).ot rule out the protective role
played by MT against toxic heavy metals and free radicals. A direct
evidence in support of such a role is given by the observation that divalent
metals like cadmium and zinc are known to induce MT synthesis by
increasing the level of MT gene expression [16,17]. In addition, several
other organic compounds, oxidative stress and inflammatory conditions
have been shown to induce MT synthesis [18-20]. Recently, a number of
evidences have assessed the importance of MT by using mice with null
alleles of MT genes [21]. These results confirm the role of MT in the
homeostasis of heavy metals and its participation in the control of heavy
metal and free radical toxicity.
In this review, we present the results of our studies on MT in Antarctic
fishes. As these organisms have remained isolated south of the Antarctic
Convergence for more than 20 million years, they may represent a useful
tool to study the strategies evolved to adapt themselves to particularly
severe environmental conditions.
The Zinc Status in Antarctic Fish
We have investigated the status of hepatic zinc in different species of
Nothothenioidei by determining the intracellular levels ofMT. We found
a large difference in MT content between the hemoglobinless
Channichthyidae and the red-blooded Nothothenidae. The results in Table
1 show the levels of MT (expressed in I-lg/mg protein) in acetone powder
preparations obtained from hepatic tissues of Chionodraco hamatus,
Chionodraco rastrospinosus, Chaenocephalus aceratus and Trematomus
bernacchii. In the three icefish, the MT levels varied from a minimum of
0.002 /-lg MT/mg protein in C. aceratus to a maximum of 0.2 /-lgMT/mg
protein in C. hamatus, whereas in the red-blooded T. bernacchii, the MT
content was significantly higher.
Despite these marked differences in MT content, all the species
investigated showed significant levels of protein-associated zinc, of which
part was recovered in a high-molecular weight and part in a lowmolecular weight protein fraction, as shown by the chromatographic
profiles reported in Fig. 1.
As most of the metal-binding proteins possibly involved in zinc
homeostasis are low-molecular weight proteins, we focused our attention
on the protein fraction included into the resin. Indeed, the low~molecular
weight zinc-containing fractions eluted from the G-75 columns were
purified by a combination of anion-exchange chromatography and HPLC.
V. Carginale et al.
support a metal storage function of MT, which may acquire a particular
relevance at specific stages of organism life, such as embryonic
development and growth [15]. This does 1).ot rule out the protective role
played by MT against toxic heavy metals and free radicals. A direct
evidence in support of such a role is given by the observation that divalent
metals like cadmium and zinc are known to induce MT synthesis by
increasing the level of MT gene expression [16,17]. In addition, several
other organic compounds, oxidative stress and inflammatory conditions
have been shown to induce MT synthesis [18-20]. Recently, a number of
evidences have assessed the importance of MT by using mice with null
alleles of MT genes [21]. These results confirm the role of MT in the
homeostasis of heavy metals and its participation in the control of heavy
metal and free radical toxicity.
In this review, we present the results of our studies on MT in Antarctic
fishes. As these organisms have remained isolated south of the Antarctic
Convergence for more than 20 million years, they may represent a useful
tool to study the strategies evolved to adapt themselves to particularly
severe environmental conditions.
The Zinc Status in Antarctic Fish
We have investigated the status of hepatic zinc in different species of
Nothothenioidei by determining the intracellular levels ofMT. We found
a large difference in MT content between the hemoglobinless
Channichthyidae and the red-blooded Nothothenidae. The results in Table
1 show the levels of MT (expressed in I-lg/mg protein) in acetone powder
preparations obtained from hepatic tissues of Chionodraco hamatus,
Chionodraco rastrospinosus, Chaenocephalus aceratus and Trematomus
bernacchii. In the three icefish, the MT levels varied from a minimum of
0.002 /-lg MT/mg protein in C. aceratus to a maximum of 0.2 /-lgMT/mg
protein in C. hamatus, whereas in the red-blooded T. bernacchii, the MT
content was significantly higher.
Despite these marked differences in MT content, all the species
investigated showed significant levels of protein-associated zinc, of which
part was recovered in a high-molecular weight and part in a lowmolecular weight protein fraction, as shown by the chromatographic
profiles reported in Fig. 1.
As most of the metal-binding proteins possibly involved in zinc
homeostasis are low-molecular weight proteins, we focused our attention
on the protein fraction included into the resin. Indeed, the low~molecular
weight zinc-containing fractions eluted from the G-75 columns were
purified by a combination of anion-exchange chromatography and HPLC.