Biochemical and Histopathological Effects of Aflatoxin on ...

4.5 The Antioxidant Defense Mechanism
To counter the harmful effects <strong>of</strong> ROS, antioxidant defense
mechanism operate to detoxify or scavenge these reactive oxygen species.
The antioxidant system comprises <strong>of</strong> different types <strong>of</strong> functional
components classified as first line, second line <strong>and</strong> third line defenses.
4.6 Preventive Antioxidants - First Line Defense
The first line defense comprises preventive antioxidants that act by
quenching <strong>of</strong> Oz, decomposition <strong>of</strong> HzOz <strong>and</strong> sequestration <strong>of</strong> metal ions. The
antioxidants belonging to this category are enzymes like superoxide
dismutase (SOD), catalase, glutathione peroxidase <strong>and</strong> glutathione reductase
<strong>and</strong> non-enzymatic molecules like minerals <strong>and</strong> some proteins.
(a) Superoxide dismutase (SOD) (E.C.l.15.1.1)
SOD mainly act by quenching <strong>of</strong> superoxide (02.') , an active oxygen
radical, produced in different stages <strong>of</strong> aerobic metabolism (Meier et al,
1998; MacMillan-Crow et al, 1998; Yamakura et al, 1998; LiY et al, 1995;
Kizaki et ai, 1997)
Different enzymes <strong>of</strong> SOD are described. The one present m the
mitochondria is Mn z + dependent, that present in the cytoplasm is
independent. An extra cellular Cu-Zn dependent enzyme is also reported
(Halliwell <strong>and</strong> Gatteridge, 1985; Fridovich, 1989).
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