The striated and smooth adductor muscle tropomyosins (TMs) of Yesso scallop Mizuhopecten yessoensis have been known to express different isoforms, but have not been characterized in detail to date. In the present study, TMs from both muscles of Yesso scallop were purified and their stabilities were compared by circular dichroism (CD) spectrometry and differential scanning calorimetry (DSC). From the CD data, the apparent melting temperature and the apparent free energy of folding at 20°C were calculated to be 30.5°C and -13.4 kJ/mol, and 36.0°C and -31.9 kJ/mol for the striated and smooth muscle TMs, respectively. From the DSC data, ΔH values were calculated to be 1.87 × 103 and 2.19 × 103 kJ/mol for striated and smooth muscle TMs. These results suggest that smooth muscle TM has higher thermostability than striated muscle TM. The amino acid residues responsible for such stability difference were considered to be the six amino acid substitutions in the middle region of the TM molecules.
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