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In-Depth Information
HNO
2
+
HNO
3
OH
H
2
O
NO
2
NO
2
O
2
tyrosyl,O
2
CH
2
CH
NH
OC
HbO
2
metHb
+
NO
3
−
NO
O
2
, RSH
O
2
−
RSNO
LnM
ONOO
−
(peroxynitrite)
LnMNO
LnM = [Fe
4
S
4
] aconitase, IRP, FNR, and SOXr
LnM = Fe(por) soluble guanyl cyclase, Hb, COX
LnM = Fe(II) ferritin, RNR
Figure4.6
Achemicalhierarchyofnitricoxide'sbiologicaltargets.
gas it does not need active transport to cross cell and organelle membranes, and since it readily permeates
most macromolecules it is impossible to use conventional genomic or molecular biology techniques to
determine its target cells or macromolecules. The biochemical universe of possible targets is wide open
to nitric oxide and there is no “consensus sequence” or structure to search or screen for its targets with
genomic or proteomic techniques. So to answer the question “what are nitric oxide's biological targets?”,
its chemistry and those species with which it reacts most rapidly have to be understood. Based on these
latter considerations, a general set of possible targets is shown in Figure 4.6.
139
Of these reactions, its
reaction with superoxide is the fastest,
140
and that with oxyhemoglobin the most pervasive.
141
The reaction
of nitric oxide with thiol to give RSNO requires an electron acceptor.
142
4.9 General reactivity patterns
A summary of the general reactions for monomeric nitric oxide is shown in Figure 4.7.
4.9.1 Oxidation
Nitric oxide is readily oxidized and a variety of stable nitrosonium salts including tetrafluoroborate, per-
chlorate, and hydrosulfate are available.
143
Indeed, [NO]HSO
4
is an intermediate in the lead chamber
process for the manufacture of sulfuric acid. Although the nitrosonium salts are hydrolytically sensitive,
they can be handled briefly in solvents such as methanol.
144
Base-promoted addition of water, alcohols,
and amines leads to either nitrite, alkylnitrites, or nitrosamines. Nitrosonium salts are also good outer
sphere one-electron oxidants and are useful in cases where the gaseous nitric oxide product can easily be
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