Molecular Field analysis of the actin-myosin interaction.

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Recently a ratchet model has been proposed for the molecular mechanism of actomyosin sliding where unidirectional thermal diffusion of myosin head takes place along asymmetric molecular field of actin filament. The purpose of the present research is to obtain experimental evidence for asymmetric molecular field along myofilaments. Firstly the contractility of single myofibrils was studied under isometric conditions (Yuri et al., 1998), and then during shortenings (submitted). Then the surface molecular field of myofibril was studied by use of an atomic force microscope to obtain transverse elasticity distribution along sarcomere (Yoshikawa et al., 1999). By analysing the longitudinal and transverse elesticities of myofibril, we found the elasticity of single attached cross-bridge has the structural asymmetry (in preparation). To study the molecular field along actin and myosin filaments in detail, trials were made to prepare cantilever with a ZnO wisker and obtain AFM images of actin and myosin filaments by use of this cantilever. Separately, by use of a laser tweezer system, single actin filament was suspended between two immobilized beads, and a bead coated with myosin was made to slide along the actin filament. By analysing the movements of myosin-coated beads along actin filament, the molecular field present between actin and myosin interface was examined. These studies supported the presence of asymmetric molecular field along myofi1aments, which is in accord with the ratchet theory. Further detailed studies of internal structures of the molecular field of myofilaments are required to clearly the molecular mechanism of muscle contraction.