The structure of actin filaments and the origin of the axial periodicity in the I -substance of vertebrate striated muscle

Abstract Certain advances due mainly to H. E. Huxley (see Huxley 1961, 1963) have made it possible to use the electron microscope to study the detailed structure of the filaments in the contractile apparatus. The results of our work on actin filaments have already been published (Hanson & Lowy 1962, 1963). We shall now examine some of the consequences of these findings, including certain unsolved problems which they raise. Actin in the polymerized form (F-actin) has been prepared from rabbit skeletal muscle by the usual methods and examined in negatively stained preparations in the electron microscope (Hanson & Lowy 1963). It has been found that solutions of F-actin are, in fact, suspensions of filaments. These consist of globular subunits arranged in a characteristic helical manner (figure 15).