Chemistry Reference
In-Depth Information
(a)
∆
A
0.04
0.025
(b)
0.02
(c)
0.020
0.00
0
100
200
300
Time (
µ
s)
0.015
0.010
0.005
10
µ
s
100
µ
s
804
µ
s
0.000
350
400
450
500
550
600
λ
(nm)
Figure 5.8.
Transient absorption spectrum obtained on pulse radiolysis of N
2
O-
saturated aqueous solution containing native BSA (1 × 10
−4
M) and HCO
3
(0.5 M) at
pH 8.8. Inset: transient absorption profiles under identical conditions at (a) 410 nm, (b)
510 nm, and (c) 600 nm. dose = 25 gy (adapted from Joshi and Mukherjee [59] with
the permission of Elsevier Inc.).
•−
•
2
−
+
BSA TrpH TyrOH . CO
(
,
…
+
)
(
600
nm
)
→
BSA CO
+
+
H
(5.15)
3
3
BSA Trp TyrOH
(
•
,
,
…
.) (
51 nm
0
)
→
BSA TrpH TyrO
(
,
•
,
…
.) (
410
nm
)
1
1
(5.16a)
BSA Trp TyrOH
(
•
,
,
… +
.)
BSA TrpH TyrOH
(
,
,
…
)
1
2
(5.16b)
→
BSA TrpH TyrOH
(
,
… + BSA TrpH TyrO
.)
2
(
,
•
…
.).
1
The formation of BSA
•
was also seen in the oxidation of oxymyoglobin and
oxyhemoglobin by
CO
•−
, which had rate constants in the range of 5.7 × 10
7
/M/s
to 5.2 × 10
7
/M/s [58]. The BSA
•
radical further oxidized the Fe
II
center through
both intra- and intermolecular forces. The reactions of
CO
•−
with nitrosyl(II)
hemoglobin (HbFe
II
NO) and nitrosyl(II)myoglobin (MbFe
II
NO) have also
been carried out (Table 5.2). Both reactions proceed through two steps (Eqs.
5.17 and 5.18). The outer-sphere oxidation of nitrosyl iron(II) proteins pro-
ceeds to their corresponding nitrosyl iron(III) forms (Eq. 5.17), followed by
dissociation to NO
•
(Eq. 5.18):
MbFe NO CO
II
+
•−
→
MbFe NO CO
III
+
2
−
(5.17)
3
3
MbFe NO H O MbFe OH NO
III
+
→
III
+
•
.
(5.18)
2
2
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