PUREALIN BLOCKS THE SLIDING MOVEMENT OF SEA-URCHIN FLAGELLAR AXONEMESBY SELECTIVE-INHIBITION OF HALF THE ATPASE ACTIVITY OF AXONEMAL DYNEINS

Ciliary and flagellar movements are explained by active sliding betwee n the outer doublet microtubules of an axoneme via their inner and out er dynein arms. Purealin, a novel bioactive principle of a sea sponge Psammaplysilla purea, blocked the motility of Triton-demembranated sea urchin sperm flagella within 5 min at concentrations above 20 mu M. I n a similar concentration range, purealin blocked the sliding movement of the flagellar axonemes in vitro within a few minutes judging from the turbidity measurements. The ATPase activity of axonemes was partia lly inhibited by purealin in a concentration-dependent manner. The max imum inhibition reached approximately 50% at concentrations above 20 m u M, indicating that half the axonemal ATPase activity is sensitive to purealin. Similar results were observed on the ATPase activity of out er-arm-depleted axonemes and that of a mixture of 21S dynein and salt- extracted axonemes. On the other hand, ATPase activity of isolated 21S dynein was not inhibited by purealin. The inhibitory action of pureal in on the axonemal ATPases was reversed by dilution of purealin. The e ffect of purealin on the double-reciprocal plot of the ATPase activity as a function of ATP concentrations showed that the inhibition was no t a competitive type. In accord with this finding, purealin did not af fect the vanadate-mediated UV photocleavage of axonemal dyneins. These results suggest that purealin binds reversibly to a site other than t he catalytic ATP-binding site and inhibits half the ATPase activity of axonemes. Taken together, our results suggest that purealin-sensitive ATPase activity of the dynein arms plays an essential role in generat ing the sliding movement of flagellar axonemes.