Structural and Thermodynamic Properties of Tropomyosins from the Ordinary and Hybrid Tilapia

Tilapia is a very common aquaculture species in Taiwan and both the so-called freshwater tilapia (Oreochromis niloticus) and seawater tilapia (O. mossambica) are available. In order to characterize muscle tropomyosin from these tilapia and hybrid ones (O. mossambica × O. niloticus ), the biochemical properties of tropomyosin among these tilapia species were analysed. The nucleotide sequences of tropomyosin genes were determined by cDNA cloning, and the amino acid sequences were deduced. Fast skeletal muscle tropomyosins were isolated by the combination of isoelectric point precipitation and salting out with ammonium sulfate. The thermodynamic properties of the purified tropomyosins were examined by differential scanning calorimetry (DSC) and circular dichroism (CD) spectrometry. The results showed that those tropomyosins were identical to each other including the deduced amino acid sequence, thermodynamic patterns as measured by DSC and CD, except the partial differences in the nucleotide sequence, namely, at 99th (A/G), 183rd (T/C) and 846th (T/C) positions in the open reading frame.