EXPERIMENTAL FIGURE 17-29 Myosin V has a step size of 36 nm, with each head stepping hand-over-hand in 72-nm steps. (a) Researchers have managed to label the neck of just one head of myosin V and follow its movement down an actin filament with nanometer accuracy (see Section 4.2 for how this can be achieved). (b) Trace of the label on one myosin V molecule as it walks down an actin filament. The labeled myosin head takes successive 72-nm steps. When the label was attached to the tail, the myosin V motor as a whole was found to take 36-nm steps (not shown). Thus myosin V heads step hand-over-hand down an actin filament in 72-nm steps for each head, but with the motor as a whole moving 36 nm per step. As can be seen from the trace, myosin V takes many successive steps along a filament, so it is said to be processive. As shown in panel (a), the step size corresponds to equivalent sites on the helical structure of the actin filament.

[Data from A. Yildiz et al., 2003, Science 300:2061.]