The contraction of "ghost" myofibrils and glycerinated muscle fibers irrigated with heavy meromyosin subfragment-l

"Ghost" myofibrils, i.e. striated rabbit myofibrils from which myosin has been extracted, were irrigated with heavy meromyosin subfragment-l. The addition of MgATP caused contraction. The value of the isometric tension developed by glycerinated muscle fibers at rest length could be increased upon irrigation with HMM S-l. Muscles stretched to such an extent that there was practically no overlap between thick and thin filaments, generated tension after irrigation. The additional tension was probably due to the interaction between HMM S-l molecules and actin filaments in the I-bands. It is concluded that a mechanochemical force can be generated by the interaction of isolated myosin heads with actin in the presence of ATP.