Fine profile of actomyosin motility fluctuation revealed by using 40-nm probe beads.

The displacement of colloidal gold beads only 40 nm in diameter can be detected with spatial and temporal resolutions of 2.8 nm and 0.5 msec by using an optical setup in which two laser beams are reflected on the same field of a prism surface, forming interference fringes in an evanescent field adjacent to the prism surface, and the changes in scattering intensity that occur when the beads move across the fringes are measured in optical microscopic images. Results obtained when using this setup and actin-bound gold beads to measure the movement of actin filaments on myosin motor molecules revealed the fine profile of movement fluctuation and that the duty time of a single stroke of myosin motors is less than 10-20 milliseconds.