Electronmicroscopic investigation of the flexibility of F-actin.

The contour lenghts and the end-to-end distances of a large number of F-actin filaments were measured in electronmicrographs. Preparation of F-actin for electron-microscopy was made at three different temperatures. The flexibility parameter or the elastic modulus for bending of F-actin was determined from the relation between the contour length and the end-to-end distance after statistical treatment. The value of the flexibility parameter obtained here showed good agreement with that obtained by the quasielastic light scattering at all temperatures examined. The flexibility of F-actin increased with raising temperature and with the binding of heavy meromyosin.