Van't Hoff and calorimetric enthalpies from isothermal titration calorimetry: are there significant discrepancies?
The enthalpy of a reaction is most often determined through one of two means; it can be determined directly using calorimetry or indirectly by measuring the temperature dependence of the equilibrium constant (i.e., the van't Hoff method). Recently, discrepancies have been noted between the enthalpy measured by calorimetry, and the enthalpy determined by the van't Hoff method,. This has been suggested to indicate that the binding reaction is more complex than the simple one-to-one binding model used to describe the data. To better understand possible discrepancies between and, we have undertaken both experimental studies using isothermal titration calorimetry to measure the binding energetics of Ba(2+) binding 18-crown-6 ether and 2'-CMP binding RNase A, along with a simulation of a system involving a molecule in conformational equilibrium coupled with binding. We find that when experimental setup and analysis are correctly performed, no statistically significant discrepancies between and exist even for the linked system.
Horn
J R
JR
Department of Biochemistry, University of Iowa College of Medicine, Iowa City, IA 52242, USA.
Russell
D
D
Lewis
E A
EA
Murphy
K P
KP
D001464:Barium / Q000737:chemistry; D001665:Binding Sites; D002138:Calibration; D002151:Calorimetry / Q000379:methods*; D003568:Cytidine Monophosphate / Q000737:chemistry; D004988:Ethers, Cyclic / Q000737:chemistry; D008024:Ligands; D046911:Macromolecular Substances; D008956:Models, Chemical; D011487:Protein Conformation; D011522:Protons; D012259:Ribonuclease, Pancreatic / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics
D004988:Ethers, Cyclic; D008024:Ligands; D046911:Macromolecular Substances; D011522:Protons; D001464:Barium; D012259:Ribonuclease, Pancreatic; D003568:Cytidine Monophosphate