Designing Itc Experiments - MicroCal VP-ITC User Manual

VP-ITC MicroCalorimeter User's Manual

3.1 Designing ITC Experiments

For a ligand X binding to a single set of n identical sites on a macromolecule M, i.e.,
the single-site binding constant is
and
Where ∆G o , ∆ H o and ∆S o are the free energy, enthalpy, and entropy change for single site
binding.
By non-linear least squares fit of calorimetric titration data, the parameters K, ∆H o , and n are
determined directly in a single experiment and ∆G o and ∆S o may then be calculated. Titration
calorimetry is the only technique capable of defining all of these parameters in a single
experiment resulting in nearly complete thermodynamic characterization of the interaction.
Measuring the binding isotherm at a second temperature allows additional determination of the
change in heat capacity of binding through the relation:
M + X = MX
MX + X = MX 2
.
.
.
MX n-1 + X = MX n
[filled sites]
___________________
K =
[empty sites][X]
∆G o = —R T lnK = ∆H o -T ∆S o
∆H o T2 - ∆H o T1
___________________________
∆C p
=
T2 - T1
.
.
.
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