Limited trypsinolysis changes in structural dynamics of myosin subfragment 1

The effects of limited trypsinolysis of myosin subfragment 1 (S1) on its structural dynamics were investigated by using the method of transient electric birefringence. Conversion of S1 by trypsin to produce S1 (T) did not change the specific Kerr constant [(8.1 +/- 0.3) X 10(-7) and (8.0 +/- 0.3) X 10(-7) cm2/statvolt2 for S1(T) and S1, respectively] or the degree of alignment in a weak electric field, suggesting that the size of S1 and its permanent electric dipole moment are not modified by trypsin. On the other hand, the relaxation time for the field-free rotation, after achieving a steady-state birefringence signal, was reduced from 316 ns for S1 to 269 ns for S1(T), at 3.7 degrees C, suggesting that trypsinolysis increases the flexibility of the connections between S1 segments or introduces additional segmental motions. For both S1 and S1(T), the rate of decay for a steady-state signal was independent of the field strength, between 3.34 and 20.3 statvolt/cm. Shortening the duration of the weak electric field pulses to 0.35 microseconds, so that steady-state signals were not achieved, decreased the relaxation times for S1 and S1(T) to 240 and 210 ns, respectively, which is consistent with the segmented flexible S1 structure proposed earlier [Highsmith, S., & Eden, D. (1986) Biochemistry 25, 2237]. When the strength of the electric field was increased to above 10 statvolt/cm, in order to make the interaction energy for the S1(T) electric dipole moment in the electric field greater than the thermal energy, the relaxation time after a 0.35-microseconds pulse decreased from 210 to 170 ns as the field was increased from 7 to 20 statvolt/cm. (ABSTRACT TRUNCATED AT 250 WORDS)