Chemistry Reference
In-Depth Information
(
·ÿ
O
2
) (reaction 1). This is activation of oxygen. It should be noted that certain
chelators will facilitate reaction 1 while other chelators will not. The experimental
conditions (e.g., pH, metal to chelator ratio) will also dictate rates of reaction.
Fe + chelator ÿ! Fe (chelate)
Fe
2+
(chelate) + O
2
ÿ!
·ÿ
O
2
+ Fe
3+
(chelate)
(reaction 1)
At post-mortem pH values, there are appreciable amounts of the conjugate
acid form of superoxide (
·
OOH, neutral superoxide radical) in equilibrium with
the conjugate base form (
·ÿ
O
2
, superoxide anion radical) (pKa ~ 5) which leads
to rapid production of hydrogen peroxide (reactions 2±4)
(Halliwell and
Gutteridge, 1999).
·ÿ
O
2
·ÿ
O
2
2H
ÿ! HOOH O
2
(k < 0.3M
ÿ1
s
ÿ1
)
(reaction 2)
·ÿ
O
2
·
OOH H
ÿ! HOOH O
2
(k = 9:710
5
M
ÿ1
s
ÿ1
)
(reaction 3)
·
OOH
·
OOH ÿ! HOOH O
2
(k = 8:310
5
M
ÿ1
s
ÿ1
)
(reaction 4)
Hydrogen peroxide converts oxyHb to metHb (Weiss, 1982) (reaction 5).
HOOH 2oxyHb(2) 2H
ÿ! 2metHb(3) 2HOH O
2
(reaction 5)
Hydrogen peroxide is especially efficient in converting deoxyMb to metMb
(Wazawa et al., 1992, Yusa and Shikama, 1987) (reactions 6 and 7).
HOOH deoxyHb(2) ÿ! ferrylHb(4) 2OH
ÿ
(reaction 6)
ferrylHb(4) deoxyHb(2) ÿ! 2metHb(3) (reaction 7)
Hydrogen peroxide reacts with metHb and Fe
2
(chelates) to form the ferryl
heme protein radical and hydroxyl radical, respectively (reactions 8 and 9)
(Reeder et al., 2004).
HOOH metHb(3) ÿ! ferrylHb
(·+)
(4)=O H
2
O
(reaction 8)
HOOH Fe
2
(chelate) ÿ!
·
OH
ÿ
OH Fe
3
(chelate)
(reaction 9)
Both the hydroxyl radical and ferryl Hb radical can abstract hydrogen atoms
from polyunsaturated fatty acids (reactions 10 and 11) resulting in peroxyl
radical and lipid hydroperoxide accumulation (reactions 12 and 13). The
hypervalent Hb produced in reaction 11 can also abstract hydrogen atoms from
polyunsaturated fatty acids (reaction 14) and decompose LOOH to peroxyl
radicals (reaction 15) (Kanner and Harel, 1985, Reeder et al., 2004). Note that
metHb is regenerated in reactions 14 and 15.
·
OH + LHÿ! L
·
+ HOH
(reaction 10)
ferrylHb
(·)
(4)=O LH ÿ! L
·
ferrylHb(4)=O
(reaction 11)
L
·
O
2
ÿ! LOO
·
(reaction 12)
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