Yildiz, A., Forkey, J. N., McKinney, S. A., Ha, T., Goldman, Y. E. and Selvin, P. R.
Myosin V walks hand-over-hand: Single fluorophores imaging with 1.5-nm localization. Science 300: 2061-2065 (2003).

Myosin V is a dimeric molecular motor that moves processively on actin, with the center of mass moving ~37 nanometers for each adenosine triphosphate hydrolyzed. We have labeled myosin V with a single fluorophore at different positions in the light-chain domain and measured the step size with a standard deviation of < 1.5 nanometers, with 0.5-second temporal resolution, and observation times of minutes. The step size alternates between 37 + 2x nm and 37 - 2x, where x is the distance along the direction of motion between the dye and the midpoint between the two heads. These results strongly support a hand-over-hand model of motility, not an inchworm model.