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was through competing intermolecular and/or intramolecular pathways.
Overall, the pulse radiolysis experiments showed
CO
•−
was also capable of
inducing a rapid one-electron oxidation of thiols and tyrosine phenolic groups
in addition to reducing exposed disulfide bonds of the protein [80].
5.2 NITROGEN SPECIES
5.2.1 Nitrogen Monoxide
Nitrogen monoxide (nitric oxide,
•
NO) was previously considered a toxic to
the environment, destroying ozone and causing acid rain [81, 82]. In 1987,
•
NO
was discovered to be formed by enzymatic reactions in a variety of mammalian
cells [83]. This has led to numerous biological chemistry studies on this mol-
ecule [82, 84-91]. The generation of
•
NO at low physiological levels is involved
in processes such as blood pressure modulation, immune system control, peri-
stalsis, and neurotransmission [92-96]. Sources of the production of
•
NO in
biological systems are given in Figure 5.10. These include (1) reduction of
NO
−
with various metalloprotiens, (2) reduction of organic nitrates, (3) nonenzy-
matic reduction of
NO
−
, (4) oxidation of L-arginine to L-citrulline by nitric
oxide synthase (NOS), and (5) nitrite reduction by nitrite reductase (NOR).
•
NO may be transformed to
NO
−
, peroxynitrite, and N
2
O by the reactions
mediated by the metal ion center of proteins (Eqs. 5.22-5.24) [84, 97, 98]:
Figure 5.10.
Chemistry of •NO
(g)
: sources of production in biological systems, its func-
tions and roles, and multiple oxidation and reduction pathways, leading to the forma-
tion of a variety of species that may effect a diverse range of biomolecules and
functions (adapted from Schopfer et al. [84] with the permission of the American
Chemical Society). See color insert.
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