Chemistry Reference
In-Depth Information
Using pulse radiolysis studies, a simple mechanism expressed in Equations
(4.24)-(4.27) has been proposed [98, 103, 104]:
Mn SOD OH
3
+
(
−
)
+
O
•−
(
+
H
+
)
→
Mn SOD H O O
2
+
(
)
+
k
(4.24)
2
2
2
24
Mn SOD H O O
2
+
(
)
+
•−
(
+
H
+
)
→
Mn SOD OH
3
+
(
−
)
+
H O
k
(4.25)
2
2
2
2
25
Mn SOD H O O
2
+
(
)
+
•−
→
Mn SOD H O -O
3
+
(
)
2
−
k
(4.26)
2
2
2
2
26
Mn SOD H O -O
3
+
(
)
2
−
(
+
H
+
)
→
Mn SOD OH
3
+
(
−
)
+
H O
.
k
(4.27)
2
2
2
2
27
The mechanism includes the formation of both Mn
3+
SOD and the inhibited
complex
(
+ −
.
The proposed mechanism was confirmed by conducting spectral studies in
the visible region (350-600 nm) (Fig. 4.5) [31]. The growth of the absorption
of Mn
3+
SOD was measured by reacting high concentrations of Mn
2+
SOD with
rapid generated substoichiometric amounts of
O
•−
(Fig. 4.5). In the reaction of
human Mn
2+
SOD with substoichiometric
O
•−
, there was an initial growth cor-
responding to both
Mn SOD H O -O
Mn SOD H O -O
3
(
)
)
2
2
( )
and Mn
3+
SOD with a rate constant
of 4 × 10
9
/M/s per tetramer. A slow process corresponds to the formation of
Mn
3+
SOD (Eq. 4.27). However, only the growth of Mn
3+
SOD was observed
(
k
25
= 2 × 10
9
/M/s per dimer) when
E. coli
MnSOD was used (Eq. 4.25).
3
+
2
−
2
2
Figure 4.5.
Spectra of Mn
3+
SODs (open circles) and
Mn SOD H O O
3
+
2
−
( )
(closed
circles) as measured in pulse radiolysis experiments (adapted from Abreu and cabelli
[31] with the permission of Elsevier, Inc.).
−
2
2
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