DIMERIZATION OF NATIVE MYOSIN LC2(RLC)-FREE SUBFRAGMENT-1 FROM ADULT-RABBIT SKELETAL-MUSCLE

We reinvestigated whether the native myosin LC2-free-subfragment 1 (S1 ) dimer exists by using viscometry, capillary electrophoresis, and las er light scattering. We found that the intrinsic viscosity of the mono mer is [eta](m) = 6.7 cm(3)/g and its translation diffusion coefficien t is D-t,m(20,w)(c = 0) = 4.43 x 10(-7) cm(2)/s. For the dimer, [eta]( d) = 19.8 cm(3)/g and D-t,d(20,w)(c = 0) = 2.54 x 10(-7) cm(2)/s. Usin g the Svedberg equation and introducing the values of the sedimentatio n coefficients (5.05 S for the monomer and 6.05 S for the dimer), we f ind the following molecular weights: M-r,M-m = 108 000 Da and M-r,M-d = 213 000 Da, which agree well with previous determinations. Capillary electrophoresis successfully separated S1(A1) and S1(A2), in a monome r buffer, and SI(AI) and S1(A2) and a heterodimer S1(AI)S1(A2), in a d imer buffer. An interesting feature of the monomer-dimer equilibrium i s the presence of temperature transitions, whose positions and widths depend upon the buffer conditions. At low temperatures, a pure dimer w as observed, whereas at high temperatures only the monomer was present . The dimerization site on both myosin and S1 is extremely labile.