Interactions of Tetrahymena dynein with microtubule protein. Tubulin-induced stimulation of dynein ATPase activity

The ATPase (EC 3.6.1.3) activity of 30 S dynein from Tetrahymena cilia was remarkably stimulated by porcine brain tubulin at pH 10. The activity increased with increasing concentration of tubulin until the molar ratio of tubulin dimer to 30 S dynein reached approx. 10. The optimum of the ATPase activity of 30 S dynein in the presence of tubulin was 1?2 mM for MgCl₂ and 2 mM for CaCl₂. Increasing ionic strength gradually inhibited the stimulation effects of tubulin. Activation energies of 30 S dynein in the presence and absence of tubulin were almost the same. At the temperatures beyond 25 °C stimulation effects of tubulin disappeared. ATP was a specific substrate even in the presence of tubulin. In kinetic investigations parallel reciprocal plots were observed in a constant ratio of divalent cations to ATP of 2, indicating that tubulin was less tightly bound to 30 S dynein in the presence of ATP than in the absence. The similar results were obtained at pH 8.2. 14 S dynein and the 12 S fragment which have poor ability to recombine with outer fibers were also activated with brain tubulin.