Structural stability of myosin rod from silver carp as affected by season.

:  Chymotrypsin digestion and Circular dichroism (CD) spectroscopy were used to study the structural stability of myosin rods prepared from silver carp in summer and winter. Differences in the thermal stability were clearly demonstrated by the chymotryptic digestion patterns and CD data obtained at pH 7.5 in 0.5 M KCl for myosin rods in both seasons, indicating the structural properties differed seasonally. In winter, the myosin rods were more susceptible to be cleaved into short (40 kDa) subfragments when digested at high temperature (30 °C). The major peaks in unfolding profiles showed that transition temperatures for the rods were 35 °C in winter, and 36 and 41 °C in summer. Rod subfragments (S-2 and LMM) were isolated and further analyzed by CD. In both winter and summer, the LMM fragments showed an unfolding transition at around 35.5 °C, but the S-2 fragments showed large seasonal difference; in winter, they showed a major unfolding peak around 35 °C and a minor peak at 40.5 °C, while in summer, they unfolded mostly at 44.5 °C, which was 8 °C higher than that for the LMM fragments. Short (40 kDa) S-2 subfragments isolated from winter rods gave a single unfolding transition at 41 °C. These results suggest that differences in the thermal stability of myosin rods between winter and summer were due to differences in the stability of S-2 region. Practical Application:  The aim of this study was to detect the differences in the structure thermal stability of myosin rods between summer and winter, which is a very important portion for gel formation. The information will be very useful for producing surimi from freshwater fish species in different seasons.