Skeletal muscle myosin subfragment 1 dimers

The rate of translational diffusion of skeletal muscle myosin subfragment 1 (S1) was determined from polarized dynamic light scattering autocorrelation measurements. Diffusion rates were expressed in terms of the hydrodynamic radii Rh. At 20 degrees C, in low ionic strength pH 8 solutions, Rh increased from 4.3 nm to 5.7 nm as [S1] was increased from 1.6 to 72 microM. Including MgATP to maintain S1. MgADP. Pi gave equivalent results. When the light scattering data were analyzed, assuming a monomer-dimer equilibrium, a dissociation constant of 83 microM was obtained. Steady state MgATPase activity measurements were made as a function of [ATP] for S1 in the 0.4-7 microM range, and analyzed assuming Michaelis-Menten kinetics. VMAX did not change, but KM increased about tenfold as [S1] was increased over this range. The light scattering and kinetic data were consistent with S1 aggregation at high [S1].