Regulatory role of nucleotides in axonemal function.

Axonemal sliding involves both sliding velocity and the extent of sliding, that is how many doublets slide. It is clear that axonemes cannot beat if all doublets were to slide simultaneously, thus sliding extent is important. Using the turbidimetric assay of sliding disintegration of Tetrahymena axonemes, we examined the sliding extent and th effect of APD, ATP, and ATP analogs on the sliding extent. Of course, ATP is necessary to produce sliding disintegration, but ATP alone did not produce extensive sliding disintegration. The additions of higher ATP concentration even in the presence of ADP inhibited sliding disintegration. We also observed sliding disintegration using ribose-modified ATP analogs, anthraniloylATP, and methylanthraniloylATP. The extent of sliding disintegration was proportional to the analog concentration. Thus in contrast to ATP, higher analog concentration was not inhibitory. These results indicate that high ATP concentration acts to inhibit the extent of sliding disintegration and that ADP relieves this inhibition. We propose a model in which the affinity of of multiple cooperative active sites are regulated by the binding of ATP or ADP to a regulatory site. This model provides a mechanism by which nucleotides regulate the extent of sliding necessary for effective axonemal bending.