The assembly of the rod portion of brain myosin

Electron microscopy was used to study the structural arrangement of the rod portion of brain myosin under various experimental conditions. At low ionic strength the rod formed spindle-like filaments with continuous 14 nm periodicity. In the presence of KCNS and a high concentration of CaCl2 brain myosin and its rod precipitated in a form of segments displaying both bipolar and unipolar arrangement characteristic of the myosin filaments. Limited proteolytic digestion of the rod with chymotrypsin generated several fragments of molecular masses in the range of 84 kDa to 30 kDa. The 74 kDa fragment appeared to be the shortest one which preserves the ability to form filaments.