A Calorimetric Study of Ca²⁺-and Mg²⁺-Binding by Calmodulim

Abstract

Enthalpy titrations of calmodulin with Ca²⁺ (or Mg²⁺) in the presence and the absence of Mg²⁺ (or Ca²⁺) have been carried out by microcalorimetry. The binding reactions of both Ca²⁺ and Mg²⁺ to calmodulin are endothermic, indicating that the large entropy change gives rise to the strong binding of Ca²⁺ to calmodulin. The results also indicated that all the four binding sites are Ca²⁺-Mg²⁺ sites. These results are markedly different from the findings for troponin C.