ABSTRACT
A prominent feature of flagellar and ciliary motility is oscillation. Mechanical conditions influence the frequency of oscillation. Within a beating flagellum, regardless of the presence of ATP the activity of dynein arms except those of the doublet microtubules on the two sides of the central-pair is kept low, indicating oscillation requires several modes of dynein activity. Experiments by using dynein arms (21S dynein) isolated from sea urchin sperm flagellar axonemes suggest that the dynein molecule is not only responsible for the oscillatory force generation but also capable of changing its mode under mechanical signal of bending of the interacting microtubule. The motor activity of dynein can be modified by forced bending of the interacting doublet. A possible mode change from a forward to a backward also occurred in dyneins, still attached on the doublet, as a transient event upon an application of the mechanical signal of bending.
