Biomedical Engineering Reference
In-Depth Information
presents a pair of redox peaks within the potential range from 0.2 to
0.8 V in deoxy-
genated PBS (pH 7.0). When a volume of air was injected into the solution, a signifi -
cant increase in the reduction peak at
0.292 V, accompanied by the disappearance of
the oxidation peak of the MbFe
III
/Fe
II
redox couple, was observed. The increase of the
reduction peak current and the shift of peak potential with an increase in the amount
of oxygen in solution indicated that Mb entrapped in MC fi lm had reacted with oxy-
gen. Oxygen can bind reversibly to heme in Mb, forming MbFe
II
ß
O
2
which can then
undergo electrochemical reduction at the potential of MbFe
III
reduction, producing
MbFe
II
again. The mechanisms can be expressed as the following:
MbFe
II
MbFe
II
O
2
→
O
2
(13)
2e
MbFe
II
O
2
2H
MbFe
II
→
H
2
O
2
(14)
The Mb-MC/EPG can also determine H
2
O
2
by CVs. When the Mb-MC/EPG was
placed in pH 7.0 PBS containing H
2
O
2
, a reduction peak at about
0.30 V was
increased and the MbFe
II
oxidation peak was decreased at the same time. However,
direct reduction of H
2
O
2
was not observed at EPG or EPG coated MC in the poten-
tial range investigated. These results are characteristic of catalytic reduction of H
2
O
2
by Mb entrapped in MC fi lm, because Mb has close structural similarity to peroxi-
dase with an intrinsic catalytic activity toward peroxide compounds. The peak reduc-
tion current of Mb-MC/EPG was linearly proportional to H
2
O
2
concentrations within
a range of 16.8-120.7
M.
Besides MC, agarose is another kind of biopolymer material often used to immo-
bilize proteins. Electrochemical catalytic reduction of H
2
O
2
using Mb-agarose/EPG
was studied by voltammetry. The reduction peak at about
µ
0.30 was increased and the
MbFe
II
oxidation peak was decreased with the addition of H
2
O
2
in pH 7.0 PBS for Mb-
agarose/EPG. However, direct reduction of H
2
O
2
could not be obtained at EPG or EPG
coated with agarose hydrogel in the potential range scanned, indicating that the reduc-
tion of H
2
O
2
was catalyzed by Mb entrapped in agarose fi lm. The reduction peak cur-
rent increased with increasing concentration of H
2
O
2
. The reduction peak currents were
linearly proportional to H
2
O
2
concentration for Mb-agarose/EPG in the range of
4.2-53.6
M. The reduction peak potential shifted negatively with increasing pH
value, suggesting that the reduction of H
2
O
2
is a proton-coupled reaction. The peak
potential depended linearly on pH in the range of 3.0-10.0 with the slope value of
28 mV pH
1
, which indicated a two-electron redox process involving one proton in the
rate-controlled step. The proposed mechanism for the reduction of H
2
O
2
by Mb can be
described as follows:
µ
Ferric Mb
H
2
O
2
→
Compound I
H
2
O
(15)
H
e
Compound I
→
Compound II
(16)
H
e
Compound II
→
Ferric Mb
(17)
NO is found
in vivo
and regulates various physiological functions including blood
pressure, platelet aggregation, and neurotransmission. NO binding to heme proteins
Search WWH ::
Custom Search