GE HEALTHCARE Biacore T100, Handbook

Page: 179 / 238

Biacore T100 Software Handbook BR-1006-48 Edition AE
179
Kinetics and affinity analysis 9
9.8 Predefined models
A set of predefined models for kinetics and steady state affinity is provided with
Biacore T100 Evaluation Software. These models are marked in the model
selection list (see Section 9.2) with a red dot, and cannot be removed or
modified.
Mass transfer parameters
All kinetic models include a term for mass transfer of analyte to the surface. If
transport is slow compared with binding of analyte to the ligand, the transport
process will limit the observed binding rate, at least partially. All models take
account of this potential limitation and can extract rate constants from the data
provided that mass transfer is not totally limiting (see Section 9.8).
The rate of mass transfer of analyte to the surface under the conditions of non-
turbulent laminar flow that prevail in the Biacore flow cell is characterized by the
mass transfer coefficient k
m
(units m
⋅
s
-1
):
One form used in fitting models in Biacore T100 is referred to as the mass
transfer constant k
t
(units RU
⋅
M
-1
⋅
m
⋅
s
-1
), obtained by adjusting the mass
transfer coefficient approximately for the molecular weight of the analyte and
for the conversion of surface concentration to RU:
A further modification of this expression gives the flow rate-independent
component of the mass transfer constant (units RU
⋅
M
-1
s
-2/3
m
-1
), referred to as
tc in the models:
where D is the diffusion coefficient of the analyte (m
2
⋅
s
-1
)
f is the volume flow rate of solution through the flow cell (m
3 ⋅
s
-1
)
h, w, l are the flow cell dimensions (height, width, length in m)
k
m
0.98 D
h
---
⎝ ⎠
⎛ ⎞
2 3 ⁄
f
0.3 w l ⋅ ⋅
----------------------
⎝ ⎠
⎛ ⎞
1 3 ⁄
=
k
t
k
m
MW 10
9
× ×
=
t
c
k
t
f
3
------
=