Agriculture Reference
In-Depth Information
Following, it is presented some biochemical biomarkers extensively used in studies of
environmental impact, including ecotoxicological analyses of the soil.
4.3.1 Enzymatic antioxidants
The use of enzymatic activity as biomarker is due to the fact that toxic compounds have high
affinity for electron pairs found in the aminoacids that form the enzymes (Cogo et al., 2009).
One of the main monitored parameters in ecotoxicological analyses of the soil is the
concentration of metals. Exposure to metals can intensify the production of reactive oxygen
species (ROS), which are normally produced in non-stressed cells and their excess can lead
to the oxidative stress and cause harmful effects (Barreiros et al., 2006).
When a cell undergoes oxidative damage, the injuries are minimized in the different
organisms by enzymatic and non-enzymatic antioxidants (Freitas et al., 2008). Among the
enzymatic antioxidants, some examples would be the superoxide dismutase, catalase,
gluthathione reductase and gluthathione -S-transferase (Mishra et al., 2006).
Superoxide dismutase catalyzes the formation of H
2
O
2
from O
2
. This enzyme was the first
discovered among the enzymatic antioxidants and, generally is one of the first to act against
damages caused by ROS (Nordberg & Arnér, 2001).
Now, the catalase function is to facilitate the removal of H
2
O
2
, degrading it in H
2
O and O
2
.
Thus, it reduces the risk of forming the radical hydroxyl from H
2
O
2
, since this oxygen
reactive species is one of the most harmful to the biological systems (Betteridge, 2000;
Diplock et al., 1998).
The metabolism of gluthathione is one of the main antioxidant defence mechanisms in the
living systems (Valko et al., 2006) and specific metals can induce the synthesis of this
compound in different species (Backor et al., 2007). In order to perform its function as
oxidant agent, gluthathione must be in its reduced form, reaction catalyzed the enzyme
gluathathione reductase (Creissen et al., 1994).
Another important defence system against the increase of free radicals involves the enzyme
gluthathione peroxidase, which acts in the removal of hydrogen peroxide and lipid
peroxides from the cell (Rover Junior et al., 2001). One of the forms of the gluthathione
peroxidase is the gluthatione-S-transferase, one of the most studied detoxicant enzymes in
different organisms, since it has an essential role in the cellular response to the stress caused
by herbicides in plants. It is considered a detoxification enzyme because it metabolizes a
great variety of xenobiotic compounds, catalyzing their conjugation with the reduced
molecule of gluthathione and forming substances of low toxicity (Malmezat et al., 2000).
According to Almeida (2003), depending on the type of contaminant and exposure period of
the organism to the contaminated environment, the activity of the antioxidant enzymes can
be stimulated or inhibited. Generally, the increase of the enzyme activity results from an
increase in the production of ROS, which leads to a exacerbated induction of enzymes; now,
the decrease can be related to prolonged exposure of the organism to environments highly
contaminated, where the production of ROS and the consequent deleterious effects of such
production surpasses the defence efforts of the organism.
Several other studies describe alterations in the enzymatic activities of the superoxide
dismutase, catalyse, gluthathione reductase and gluthathione peroxidise in different
organisms exposed to stress conditions, especially metals, corroborating their use as
effective biochemical biomarkers in the evaluation of environmental impacts (Bocchetti et
al., 2008; Cogo et al., 2009).