抄録
Biological systems structurally and functionally constitute a hierarchy from single molecules to supra-molecular assemblies, and further up to organelles, cells, and tissues. Here we focus on the hierarchical organization of biological motile systems: 1) "Bio-nanomuscle", in which a single actin filament is pulled into an A-band, a bundle of thick (myosin) filaments. This model system was invented to bridge the gap between a single-molecule system and a muscle fiber, which is considered to be a minimum unit that mimics a single (half) sarcomere of striated muscle. 2) "Single myofibril", in which mechanical properties are studied under an optical microscope. The contractile system takes either one of three states, i.e., contraction, relaxation, and self-oscillatory (SPOC) state. Here we focus on the dynamic properties of SPOC. 3) "Mitotic spindle" extracted from Xenopus eggs, which is, as we consider it, a complex system located at the highest level in the hierarchy of biomotile systems. In the experiments we used several optical microscopy techniques, such as optical tweezers and a glass microneedle. We stress that the force production due to the structural transitions in motor proteins and the molecular strain induced by the applied force are the key factors driving the self-organization in the higher-ordered biological systems. [J Physiol Sci. 2007;57 Suppl:S35]
