The Effect of Partial Extraction of Dynein Arms on the Movement of Reactivated Sea-urchin Sperm

SUMMARY Sea-urchin sperm were extracted with 0-5 M KC1 for 45 s at room temperature in the presence of Triton X-ioo, and then transferred to reactivating solution containing 1 mM ATP. The flagellar beat frequency of these KCl-extracted sperm (16 beats/s) was only about half that of control Triton-extracted sperm that had not been exposed to 0-5 M KC1 (31 beats/s), although the form of their bending waves was not significantly altered. Examination by electron microscopy showed that the extraction with 0-5 M KC1 removed the majority of the outer arms from the doublet tubules, leaving the inner arms apparently intact. By varying the duration of the KCl-extraction, it was shown that the rate of decrease in beat frequency paralleled the rate of disappearance of the arms. Prolonging the extraction time beyond 45 3 at room temperature, or 4 min at o C C, had little further effect on beat frequency. ATPase measurements suggested that 60—65 % of th e dynein in the original axonemes had been solubilized when the extraction with KC1 was permitted to go to completion. These results indicate that the generation and propagation of flagellar bending waves of essentially typical form are not prevented by the removal of the outer row of dynein arms from the doublet tubules. In terms of the sliding filament model of flagellar bending, the results suggest that the rate of sliding between tubules under these conditions is proportional to the number of dynein arms present. The lack of significant change in wave form implies that the total amount of sliding that occurs during each bending cycle is not affected by the reduced number of dynein arms, but is regulated independently in some manner by the elastic forces generated by other structures in the bent axoneme.