Biomedical Engineering Reference
In-Depth Information
TABLE 10.4
Permeability Coefficients for Compounds in Membranes
of the Plant Cell Chara ceratophylla
Permeability, m
2
/s
Compound
10
5
Carbon dioxide
4.5
10
11
Bicarbonate
5.0
10
8
Water
6.6
10
11
Urea
2.8
10
8
Methanol
2.5
10
8
Ethanol
1.4
10
9
Ethanediol
1.7
10
9
Acetamide
1.4
10
9
Formamide
2.0
10
10
Lactamide
1.5
10
9
Butyramide
5.0
10
12
Glucose
5.0
10
11
Glycerol
2.2
Source: Stein, W.,D., 1990. Channels, Carriers and Pumps. An Introduction to Membrane
Transport. Academic Press, San Diego, CA.
resulting in the efflux or exit of the molecule from the cell. Thus, the net flux of a molecule
depends on its concentration gradient. The carrier protein effectively increases the solubility
of the target molecule in the membrane.
k
Eb
A
ð
E
Þ
þ
Protein
A
$
Protein
(10.28)
%
-
Eb
k
k
Ib
A
ð
I
Þ
þ
A
$
Protein
(10.29)
Protein
%
-
Ib
k
Assuming that the binding occurs faster than the protein conformational change and
moving the molecule into the internal cell side of the membrane, one can consider reactions
(10.28)
and
(10.29)
are in equilibrium. Inside the membrane, the total concentration of the
carrier protein remains constant:
½
Protein
þ
C
AM
¼½
Protein
M
(10.30)
where C
AM
is the concentration of target species
d
carrier protein complex concentration in
the membrane and [Protein]
M
is the total concentration of carrier protein present in the
membrane. Therefore, the concentration of A inside the membrane at either side of the
membrane interface can be computed as
E
¼
C
AE
½
M
K
AE
þ C
AE
Protein
C
AME
¼½
A
$
Protein
(10.31)
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