Microcalorimetric investigations of K+- and Mg2+-induced polymerization of actin at temperatures from 293.15 K to 310.15 K

Microcalorimetric measurements of the polymerization of actin in the presence of 100 mM KCl and 2 mM MgCl2were carried out with a Calvet MS-80 microcalorimeter at temperatures from 293.15 to 310.15 K. It was observed that the polymerization of actin was endothermic and the enthalpy change for actin polymerization was temperature-dependent. The enthalpy change ΔHowas fitted to ΔHo(kJ mol-1)=434.0-1.16 (T/K) and the change in heat capacity ΔCp ocalculated from ΔHowas -1.16 kJ (mol K)-1in the above range of temperatures. The direct calorimetry results showed that the enthalpy and entropy change for actin polymerization could not be obtained from measurements of the critical concentration and the only way to assess the enthalpy change for the polymerization of actin and similar reactions lies in the use of calorimetry.