Biology Reference
In-Depth Information
sufficient to control the redox potential of the redox environment in the mitochon-
drial matrix. A detailed discussion on the redox environment of the cell has been
reviewed (Schafer and Buettner
2001
) with focus on the glutathione (GSH) and
thioredoxin systems. In order to control the redox potential, it is concluded that in
the mitochondrial matrix the only redox couple of compounds found in sufficient
amount is the GSH/oxidised glutathione (GSSG) couple. Besides, when discussing
oxidative stress and redox state the GSH system is accepted as the most important
system (Jones
2006
, Jones and Go
2010
) .
However, these three sets of redox pairs are interconnected through two simple
enzyme pathways as follows:
(a)
Transhydrogenase can interconvert the two sets of nicotinamide nucleotides:
+
+
NADP
+
NADH
NADPH
+
NAD .
(b)
GSH reductase can subsequently convert NADPH to GSH:
NADPH
++
H
+
GSSG
NADP
+
+
2GSH.
1.2.3
pH Dependence of Redox Potentials
The redox potentials for the redox pairs can now be compared in order to evaluate
the related equilibria for the redox pairs.
The redox equations for the redox pairs are as follows:
NAD
+
++
H
+
2e
−
NADH
NADP
+
++
H
+
2e
−
NADPH
GSSG
++
2H
+
2e
−
2 GSH.
As all three equations involve protons, the associated redox potentials become
pH dependent according to the Nernst equations as follows:
⎛
⎞
⎟
2
60 mV
[GSH]
⎜
EE
=−
0
log
⎟
−
60 mV·pH
(1.2)
⎜
⎟
⎜
⎟
⎜
⎝
2
[GSSG]
⎠
⎛
⎞
⎟
60 mV
[NADH]
60 mV
⎜
EE
=−
0
log
⎟
−
·pH
(1.3)
⎜
⎟
⎜
⎟
2
⎝
[NAD ]
+
⎠
2
⎛
⎞
⎟
60 mV
[NADPH]
60 mV
⎜
(1.4)
EE
=−
0
log
⎟
−
·pH.
⎜
⎟
⎜
⎟
2
⎝
[NADP
+
]
⎠
2
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