ATP-driven tubule extrusion from axonemes without outer dynein arms of sea-urchin sperm flagella

ABSTRACT We have prepared axonemes without outer dynein arms from sea-urchin (Pseudocentrotus depressus, Hemicentrotus pulcherrimus) sperm flagella by selective solubilization with NaCl. Electron microscopy revealed that the axonemes gradually lost their outer arms in 0·5 M NaCl during 10 min. Such axonemes retained 42·8 ±7·3 % of their total axonemal ATPase activity and showed C, A, D and B bands in the dynein region of 4 % SDS-gel, while a solubilized fraction of the outer arms consisted almost entirely of A band polypeptide. We have succeeded in causing extrusion of the outer doublets from such axonemes by addition of ATP and trypsin. A bundle of outer doublets was sometimes observed to be extruded first from an axoneme and to show bending motion for a while, subsequently followed by a sliding of separate doublets past each other. The speed of the tubule extrusion process was slower and around 60 % of that of intact axonemes having both types of arm. These observations indicate that the inner arms have a function equivalent to that of the outer arms, of sliding on adjacent doublets, although the inner arms seem to be constituted from polypeptide(s) different from that of the outer arms.