End-filaments: A new structural element of vertebrate skeletal muscle thick filaments

The use of low ionic strength buffers to dissociate separated thick filaments into three subfilaments is described. When the dissociation is performed in solution, rather than on an electron microscope grid, structures called end-filaments are observed where the subfilaments terminate. The end-filaments, only one of which is seen for every three subfilaments, are about 850 Å long, 50 Å wide and show transverse striations with a periodicity of 42 Å.