Biomedical Engineering Reference
In-Depth Information
Fig. 4.1
ROS formation and degradation pathways
then reduced by NADPH-dependent glutathione reductase (GR) [
97
] . GSH is also
involved in the reactions catalysed by glutathione-
S
-transferases (GST), which
conjugate GSH to various cellular metabolites and xenobiotics that are eventually
converted to mercapturic acids for excretion [
38
] :
•
−
+
+→ +
2O
2H
HO
O,
(4.9)
2
2
2
2
2H O
→+
22
2H O
O ,
(4.10)
2
2
H O
+
2GSH
→+
2H O
GSSG,
(4.11)
22
2
ROOH
+
2GSH
→+
ROH
H O
+
GSSH.
(4.12)
2
In the presence of heavy metal ions H
2
O
2
can be converted into highly toxic
·
OH
via the Fenton (
4.9
) and Haber-Weiss reactions (
4.13
-
4.15
):
(
++
n
+
n
1
•
−
Me
+
H O
→
Me
+
OH
+
OH ,
(4.13)
22
•
−
•
−
O
+
H O
→+
O
OH
+
OH ,
(4.14)
2
2
2
2
(
++
n
1
•
−
n
+
Me
+
O
→ +
Me
O .
(4.15)
2
2
Peroxiredoxins (Prx) form another family of proteins (consisting of six members
in mammalian cells) capable of reducing H
2
O
2
and alkylhydroperoxides with the
use of thioredoxin (Trx). Prx exist as homodimers with one cysteine residue per
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