Chemistry Reference
In-Depth Information
TABLE 4.7. List of Oxidized Peptides of Cyt-
c
in D
2
O and H
2
O
Parent
Modified (D
2
O)
Modified
(H
2
O)
Found on
MALDI
a
Sequence
MW Residue
δ
MW
gITW
59
K
604.3
W59
+16
620.3
M
80
IFAgIK
779.4
M80
+16
795.4
+
+
M80
+32
811.4
+
M
80
IF
82
AgIKK
907.5
F82
+16
923.5
M80
+16
923.5
cAQcH
18
TVEK
1018.4
H18
b
1032.4
+14
+
H18
b
+28
1046.4
TgPNLH
33
gLF
36
gR
1168.6
H33
−22
1146.6
+
H33
+14
1182.6
+
H33
+26
1194.6
+
H33
+32
1200.6
+
H33
+34
1202.6
+
+
F36
+16
1184.6
+
H
26
KTgPNLHgLFgR 1433.8
H26
1447.8
+14
+
H26
+32
1465.8
+
+
EETLM
65
EyLENPK
1495.7
M65
+16
1511.7
+
a
Irradiated in D
2
O.
b
Modified residue is not certain.
Adapted from Kim et al. [169] with the permission of Elsevier Inc.
a peroxo species or sulfone. Of the three His residues, only His 26 and His 33
were modified. The incorporation of O was observed, which was also identified
in a study using
H O
17
[185]. A peptide containing His 18 was modified as +14
and +28. Significantly, the HKTgPNLHgLFgK + 32 Da peptide was continu-
ally the most intense modified peptide. The Tyr residue was not modified,
resulting in observed unmodified peptides. Phe36 and Phe82 residues were
modified as Phe + 16. Phe is not reactive with
1
O
2
; hence, observed hydroxyl-
ation of residues of Phe indicates either increased reactivity at the aromatic
ring or the possibility of the involvement of a secondary oxidant (e.g., hyfroxyl
radical) during the production of and exposue to
1
O
2
[169]. Modification of
these two Phe residues by the +16 was also seen independently in exposure to
hydroxyl radicals [186].
Proteins are generally composed of 70% of dry mass of most cells in bio-
logical systems and have higher rate constants than other cellular components
for the reactions with
1
O
2
[151]. Therefore, proteins become a major target for
1
O
2
as is shown in Figure 4.12. However, the potential localization and accu-
mulation of sensitizers within particular cellular compartments (e.g., mem-
branes) and the limiting diffusion radius of
1
O
2
in the biological environment
ultimately determine a preferential attack of
1
O
2
on components of the cell
[146, 167, 187].
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