Nanoscopic analysis of the molecular field for the actinmyosin sliding.

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Recently a retchet model has been proposed for the molecular mechanism of the actomyosin sliding. This model assumes an asymmetric molecular field along actin filament over which a unidirectional thermal diffusion of myosin head takes place. The purpose of the present study is to experimentally detect possible asymmetirc molecular field along myofilaments. The experiments were made on single myofibrils, the contractile unit of skeletal muscle. The molecular field was detected by sliding microbeads on the surface of myofibrils. If an asymmetic molecular field exists on myofilaments, the microbeads may slide with reversed characteristics on the opposite sides of Z-line. Thus we prepared single myofibrils from rabbit skeletal muscle and studied their contractilities. We also developed a laser tweezer system to manupulate microbeads under optical microscope. When microbeads were approached to the surface of myofibrils attached on the surface of glass slide, they firmly adhered with each other and could not make slide by the laser tweezer. So we decided to introduce an atomic force microscope which can study the molecular field with much stronger drawing force. When the tip of cantilever of the atomic force microscope was scanned along the surface of myofibrils, the deflection signal of the cantilever was non-symmetric along the opposite sides of Z-line. Considering the myofilament polarily relative to Z-line, this finding suggests that the molecular field along the myofilament is asymmetric in accord with the ratchet theory. We plan to investigate the internal structure of the molecular field of myofilaments in future.