Chemistry Reference
In-Depth Information
Figure 14.1
Cross - linking of glycans on the
surface of different erythrocytes leads to forma-
tion of large aggregates. This process is called
hemagglutination and has been used to detect
sugar - binding (lectin) activity.
14.1
Quantitative Aspects of Lectin Affi nity
For a more quantitative determination of lectin-carbohydrate interactions, i.e., in
terms of
K
a
or
K
d
, several methods are available such as equilibrium dialysis,
isothermal calorimetry (please see Chapter 13.4), binding studies with (neo)glyco-
protein (see Table 25.1) and surface plasmon resonance (SPR) (please see Chapter
21.4.2.1). In principle, equilibrium between bound and free forms of lectins and
saccharides (i.e., affi nity constant,
K
a
) is defi ned by the following equation (also
see Figure 14.2a):
[
(
)
]
[
]
[
]
K
a
=
Lectin Saccharide complex
−
Lectin free
(
)
Saccharide
(
free
)
.
(14.1)
And
K
d
is defi ned as:
[
(
)
]
K
d
=
[
Lectin free
(
)
]
[
Saccharide free
(
)
]
Lectin Saccharide com
−
plex
.
(14.2)
Therefore,
K
d
is the inverse of
K
a
:
KK
d
=
1.
(14.3)
a
From a kinetic viewpoint, the above equilibrium consists of two processes,
association and dissociation, which are defi ned by association (
k
ass
) and dissocia-
tion (
k
dis
) rate constants.
k
k
ass
)
⎯→
⎯
←⎯
Lectin free
(
)
+
Saccharide free
(
Lectin Sacc
−
haride complex
(
)
.
(14.4)
⎯⎯
dis
When association and dissociation rates are expressed as
v
ass
and
v
dis
, respectively,
they are defi ned as follows:
