Chemistry Reference
In-Depth Information
T
1
H
+
HOO His
H
2
O
2
O
2
-
+ H
+
His Fe
3+
His
OH
-
/OH
2
k
1
His
Cys
k
2
His
k
2
´
HO His
H
2
O His
p
K
a
= 6.1
Fe
2+
H
+
His
His
Glu
His Fe
3+
His
His Fe
3+
His
His
Cys
His
Cys
H
2
O
2
His
Cys
T
2
Glu
k
3
O C
O
H
2
PO
4
-
His
Glu
Cellular
Reductants
His Fe
3+
His
His
Cys
OH
Glu
Final
p
K
a
= 9.6
O
P
OH
H
2
PO
4
-
O His
T
2P
HO His
His
Fe
3+
His
His Fe
3+
His
His
Cys
His
Cys
Figure 4.7.
catalytic cycle of superoxide reductase, showing only the observable inter-
mediates. Large arrow: reductive cycle; narrow arrows: oxidative cycle (adapted from
Pinto et al. [115] with the permission of Elsevier Inc.). See color insert.
intermediate, T1, with an absorption maximum at ca. 620 nm, which occurs at
a second-order rate constant of ∼10
9
/M/s (Table 4.4). TI intermediates have
been suggested to be ferric-(hydro)peroxo species, which decay subsequently
to another intermediate, T2, in the case of
A. fulgidus
. This step is a pseudo-
first-order, unimolecular process (Table 4.4). The optical properties of T2 are
identical to those reported for the basic form of ferric SOR [118]. T2 decays
further to the resting oxidized state through a unimolecular process for the
wild-type enzyme. This resting form was observed for the
D. vulgaris
enzyme
T1 without the formation of T2. However, both intermediates, T1 and T2, were
observed for the 1Fe-SOR from
Treponema pallidum
and 2Fe-SOR from
Desulfoarculus baarsii
[115]. The nature of intermediates T1 and T2 has been
reviewed in detail [115]. Overall, progress has been made for the last few years
on the elimination of superoxide by 1Fe- and 2Fe-SOR, but several issues still
need to be resolved. These include the number of catalytic intermediates,
reasons of low SOD activity of SOR, although thermodynamic properties
Search WWH ::
Custom Search