Introduction

Calorimetry is the only means by which one can make direct, modelindependent measurements of thermodynamic quantities. Spectroscopic techniques, despite being extremely sensitive and able to provide high-resolution structure information, can give but an indirect, modeldependent determination of the thermodynamics of a system. Calorimetric analysis therefore complements spectroscopic studies, giving a more complete description of the biological system of interest. Modern microcalorimeters are both accurate and sensitive, so that measurements require relatively small amounts of material (as little as 1 nmol) and can yield data of a relatively low uncertainty.

Diffuse heat effects are associated with almost all physico-chemical processes. Because of this, microcalorimetry provides a way of studying the energetics of biomolecular processes at the cellular and molecular level. Microcalorimetry can be used to determine thermodynamic quantities of a wide range of biological processes. Among these are: conformational change in a biological macromolecule, ligand binding, ion binding, protonation, protein–DNA interaction, protein–lipid interaction, protein–protein interaction, protein–carbohydrate interaction, enzyme–substrate interaction, enzyme–drug interaction, receptor–hormone interaction, and macromolecular assembly. Calorimetry is also useful in the analysis of the thermodynamics of very complex processes, for example enzyme kinetics and cell growth and metabolism. That is, calorimetry is not narrowly applicable to processes occurring at equilibrium.

There are three broad classes of biological calorimetry: bomb calorimetry, differential scanning calorimetry (DSC) and isothermal titration calorimetry.