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  • Author or Editor: Sz. Halasi x
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Summary  

The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of these proteins as well.

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Summary  

In our present study we performed the detailed characterisation of jasplakinolide and phalloidin on the thermal stability of actin filaments. The heat absorption curves were analysed by using the model established by Sanchez-Ruiz et al. [1]. The analysis provided the activation energies attributed to the heat denaturation of actin filaments in the absence and in the presence of toxins. The results indicated that there are kinetic differences between the toxin-mediated stabilization of the Ca2+-and Mg2+-actin filaments. The effect of toxins appeared to be cation dependent.

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Summary  

The effect of pH was characterised on the thermal stability of magnesium saturated skeletal and cardiac α-actin isoforms with differential scanning calorimetry (DSC) at pH 7.0 and 8.0. The calorimetric curves were further analysed to calculate the enthalpy and transition entropy changes. The activation energy was also determined to describe the energy consumption of the initiation of the thermal denaturation process. Although the difference in T mvalues is too small to interpret the difference between the a-actin isoforms, the values of the activation energy indicated that the α-skeletal actin is probably more stable compared to the α-cardiac actin. The difference in the activation energies indicated that lowering the pH can produce a more stable protein matrix in both cases of the isoforms. The larger range of the difference in the values of the activation energies suggested that the α-cardiac actin is probably more sensitive to the change of the pH compared to the α -skeletal actin.

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