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O
O
O
O
O
O
3
O
3
S
S
S
OH
OH
OH
O
NH
2
NH
2
NH
2
Methionine
Sulfoxide
Sulfone
NH
2
HO
NH
2
HO
S
NH
2
O
3
S
O
SH
O
HO
O
Cysteine
Cystine
O
O
H
2
N
O
O
NH
O
3
N
OH
C
NH
OH
NH
2
H
O
HN
Histidine
2
-
Amino
-
N
-
formylureido
-
succinamic acid
O
-
O
O
C
O
O
O
3
O
3
NH
2
OH
OH
NH
2
NH
H
NH
2
O
NH
2
H
O
Tryptophan
Kynurenine
N
-Formylkynurenine
O
O
OH
O
3
OH
NH
2
NH
2
O
HO
O
Tyrosine
2
-
Amino
-
3
-
(3,4
-
dioxo
-
cyclohexa
-
1,5
-
dienyl)
-
propionic acid
Figure 4.16.
Ozone reactions with Met, cys, His, Trp, and Tyr (adapted from Sharma
and graham [15]).
The ozonolysis of peptides containing residues of Tyr and His, angiotensin
II (DRV
y
I
H
PF) and two analogues (DRV
y
I
A
P
A
and DRV
A
I
H
PA) has
been carried out to characterize carbonyl products in order to understand the
mechanisms of ozonolysis of biomolecules [231]. The second-order rate con-
stants,
k
, for reactions with O
3
were determined as (4.39 ± 0.34) × 10
2
/M/s,
(2.74 ± 0.03) × 10
2
/M/s, and (3.79 ± 0.03) × 10
2
/M/s for angiotensin II, DRV
y-
I
A
P
A
, and DRV
A
I
H
PA, respectively. Reaction rate constants suggest that the
atmospheric lifetime of these peptides would be 20-30 days [231]. The major
oxidized products identified were His + 3O, Tyr + O, and Phe + O. Two other
adducts, Tyr + 3O and Tyr + 34, were also observed. The minor products
include His + 5, His + 34, and His + 82, which suggests a continued oxidation
of the products and of nonspecific sites of the parent peptide. Fragmentation
mechanisms of the oxidized peptides in angiotensin II were interpreted using
SID FT-IcR MS/MS experiments, Rice-Ramsperger-Kassel-Marcus (RRKM)
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