PROTEASE SUSCEPTIBILITY OF FAST SKELETAL MYOSIN HEAVY-CHAIN FROM CARPACCLIMATED TO COLD AND WARM TEMPERATURES

Myosins and their rod fragments from fast skeletal muscles of carp acc limated to 10 and 30 degrees C were digested with alpha-chymotrypsin. Myosins in 0.12 M NaCl were digested at 10 degrees C with the protease at an enzyme-to-myosin weight ratio of 1/100 which cleaved mainly the region connecting myosin subfragment-1 and rod. When relative amounts of remaining myosin heavy chain band from the 10 degrees C-acclimated carp were plotted on a logarithmic scale against reaction time, diges tion was found to proceed in the first order reaction with 4.2 x 10(-4 ) s(-1), which was lower than 6.1 x 10(-4) s(-1) for the 30 degrees C- acclimated carp (P < 0.05). The other region, which is susceptible to protease and located between myosin subfragment-2 and light meromyosin , was examined at 10 degrees C using myosin rod in 0.5 M KCl and alpha -chymotrypsin with an enzyme-to-rod weight ratio of 1/120. Both myosin rods from the 10- and 30 degrees C-acclimated carp gave about 2 x 10( -4) s(-1), with no differences in protease susceptibility. These resul ts are in marked contrast to our previous observation that myosin from the 10 degrees C-acclimated carp is less thermostable in the crossbri dge head and alpha-helical region of the rod part than that from the 3 0 degrees C-acclimated carp.