Biomedical Engineering Reference
In-Depth Information
OR
IGF-I
IGF-II
FIGURE 11.12
IGF-I and -II competitively bind to six IGFBPs to form corresponding
complexes.
binding proteins in that it displays a 20- to 100-fold higher anity for IGF-
II than IGF-I [69, 72, 74-76]. We can then reasonably assume that the six
IGFBPs in the cartilage can be described by two functional groups. That is,
one group binds IGF-I and II with equal anity (e.g., IGFBP 1-5), and the
other group has high IGF-II binding preference but low IGF-I anity (e.g.,
IGFBP-6) [34].
11.4.2 Model Development for a Competitor
Growth Factor
The reactive-transport model shown in the previous sections will now be fur-
ther extended to include competitive binding of IGF-I and -II to a family of
six IGFBPs attached to the ECM.
Let IGF
j
be used to represent the two growth factors (i.e., IGF-I and -II),
IGFBP
i
represent the two functional groups of IGFBPs;
k
+
ji
represents the
association rate constant of each growth factor with each of the two IGFBP
functional groups; and
k
−ji
the dissociation rate constant of each growth
factor with each IGFBP functional group. With the nomenclature the chemical
reaction between IGFs and IGFBPs can be e
ciently described as
IGF
j
+ IGFBP
i
k
+
ji
k
−ji
IGF/IGFBP
ji
,j
=1
,
2;
i
=1
,
2
(11.48)
←→
Thus, with analogy to equation (11.31), the total concentration of IGF-I
and -II (
c
j
) in cartilage is assumed to be composed of free IGF (
c
j
) and
its immobile complexes (
c
ji
) attached to two functional groups of IGFBPs.
That is,
6
c
j
=
c
j
+
c
ji
,j
=1
,
2
(11.49)
i
=1
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