Thermodynamic characterization of muscle tropomyosins from marine invertebrates

Structural properties of invertebrate muscle tropomyosin (TM) have not been characterized in detail to date. TMs were thus purified from the mantle muscle of Japanese common squid Todarodes pacificus, the foot muscle of tokobushi abalone Haliotis diversicolor and the tail muscle of kuruma prawn Marsupenaeus japonicus, and investigated for their thermodynamic properties by circular dichroism (CD) spectrometry and differential scanning calorimetry (DSC). From the CD spectrometry data, the apparent melting temperature and the apparent free energy of unfolding at 20 °C were calculated to be 43.5 °C and 14.5 kJ/mol for the squid TM, 43.0 °C and 23.9 kJ/mol for the abalone TM, and 47.3 °C and 50.2 kJ/mol for the prawn TM, respectively. From the DSC data, the total free energy of unfolding at 20 °C was calculated to be 129 kJ/mol, 253 kJ/mol, and 271 kJ/mol for the squid, abalone, and prawn TMs, respectively. These results suggest that the thermal stability was in the order of prawn TM > abalone TM > squid TM.