Fig. 4. Velocity of microtubule sliding and sliding disintegration in elastase-treated flagella. (A) Movie images with tracings (top panels) showing sliding of singlet microtubules interacted with dynein arms exposed on the thinner (left panels) and the thicker (right panels) bundles of doublets obtained by splitting between the bundles in quiescent flagella. The microtubules moved away from the head after a UV flash. (B) Distribution of sliding velocities of singlet microtubules on the thinner (left) and thicker (right) doublet bundles at 1 mM caged-ATP and 10^–4 M Ca²⁺. The velocity on the thicker bundles was significantly lower than that on the thinner bundles. (C) Average sliding velocities with their standard deviations (bars) measured in forward (FW) and backward (BW) sliding with and without imposed bending in axonemal fragments (left graph), in the quiescent flagella severed at the basal P-bend (middle graph) and in the quiescent flagella (right graph). Asterisks indicate that the differences between the two are statistically significant (Mann-Whitney U test, ^**P<0.01; ^*P<0.05).