Isothermal titration calorimetry

AI Thread Summary
Isothermal titration calorimetry was used to calculate the binding enthalpy (\DeltaH^{o}_{bind}) of a protein-ligand interaction, yielding a value of -5000 cal/mol at 25°C. The equilibrium ligand binding was measured at both 25°C and 37°C, with various ligand concentrations and corresponding equilibrium concentrations. The user initially calculated the dissociation constant (K_d) graphically and found the standard Gibbs free energy change (\DeltaG^{0}) to be -12300.1 cal. They expressed uncertainty about how to derive the binding entropy (\DeltaS^{0}_{bind}) at 37°C from this information. Ultimately, they realized that using the van't Hoff equation would allow them to determine \DeltaH at 37°C and subsequently find \DeltaS^{0}_{bind}.
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Homework Statement



Using isothermal titration calorimetry, you calculate \DeltaH^{o}_{bind} (= -5000 cal/mol) for a protein-ligand binding reaction at 25°C. You then perform a separate assay in which you measure equilibrium ligand binding at two different temperatures:

L_{0} (nM) Ceq (nM) at 25°C Ceq (nM) at 37°C
0.01 :: 0.007 :: 0.006
0.03 :: 0.021 :: 0.017
0.1 ;: 0.070 :: 0.058
0.3 :: 0.197 ;: 0.166
1 :: 0.537 :: 0.439
3 ;: 0.830 :: 0.778
10 :: 0.943 :: 0.930
30 :: 1.002 :: 0.964
100 :: 0.981 :: 1.009

What is \DeltaS^{0}_{bind} at 37C

Homework Equations


\DeltaG^{0}=RTlnK_{D}

\DeltaG=\DeltaG^{0} + RTln[L]_{eq}/[P]_{eq}[L]_{eq}

\DeltaG=\DeltaH-T\DeltaS


The Attempt at a Solution



I can find K_{d} graphically and therefore find \DeltaG^{0} to be -12300.1 cal. At the same temperature, \DeltaG^{0}=\DeltaG at 25C, so i can find \DeltaS at 25C. But I don't know how this helps me find \DeltaS^{0}_{bind} at 37C or if this helps me at all.

thanks for any help or direction
 
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never mind, I think i figured it out using the van't hoff equation to find delta H at 37C since I can find the different Kds and am given the different temperatures.
 
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