Dynein couples the energy of ATP hydrolysis to drive the sliding of adjacent microtubule doublets in the axonemes of eukaryotic cilia and flagella. Due to large size of dyneins and their complex composition, it has been difficult to define the interaction of dynein and tubulin dimer. We have prepared two fragments containing the motor domain of β- and γ-heavy chins of outer arm dynein from Tetrahymena cilia. In the present study, conformational changes of the fragments were examined by using acrylodan, a cysteine-specific fluorescence probe. ATPase activities of acrylodan-modified fragments were stimulated to 2-3 times in addition to bovine brain tubulin dimer. Binding of tubulin dimer to acrylodan-modified fragments induced a large blue shift in fluorescence emission couples with ATP hydrolysis. The results of the present study indicate that dyneins cause conformational changes because acrylodan demonstrated a blue-shifted emission spectrum on exposure to a hydrophobic environment.