Abstract
Axonemal dyneins are force‐generating ATPases that produce ciliary and flagellar movement. A dynein has large heavy chain(s) in which there are multiple (4–6) ATP‐binding consensus sequences (P‐loops) as well as intermediate and light chains, constituting a very large complex. We purified a monomeric form of dynein (dynein‐a) that has at least three light chains from 14S dyneins of Tetrahymena thermophila and characterized it. In in vitro motility assays, dynein‐a rotated microtubules around their longitudinal axis as well as translocated them with their plus‐ends leading. ATPase activity at 1 mM ATP was doubled in the presence of a low level of ADP (≥ 20 μM). Both ATPase activity and translocational velocities in the presence of ADP (≥ 20 μM) fit the Michaelis‐Menten equation well. However, in the absence of ADP (< 0.1 μM), neither of the activities followed the Michaelis‐Menten‐type kinetics, probably due to the effect of two ATP‐binding sites. Our results also indicate that dynein‐a has an ATP‐binding site that is very sensitive to ADP and affects ATP hydrolysis at the catalytic site. This study shows that a monomeric form of a dynein molecule regulates its activity by direct binding of ATP and ADP to itself, and thus the dynein molecule has an intramolecular regulating system. Cell Motil. Cytoskeleton 49:189–199, 2001. © 2001 Wiley‐Liss, Inc.