The substrate specificity of dynein from Tetrahymena cilia

The substrate specificity of the 22S dynein ATPase from Tetrahymena cilia was investigated. The 22S dynein exhibited a high specificity for ATP in terms of both apparent Km and Vmax: naturally occurring nucleoside triphosphates other than ATP were hydrolyzed slowly with an apparent Km of 0.25-1 mM, a sharp contrast to that of ATP hydrolysis (1-4 microM). Pyrophosphate was a poor inhibitor for the dynein ATPase, indicating weak affinity. Since dynein binds ATP tightly and hydrolyzes it at a high rate, a method to determine a trace amount of ATP in the presence of other nucleoside triphosphates has been developed by taking advantage of this enzymatic characteristic of dynein. The effect of P1,P5-di(adenosine-5'-)-pentaphosphate (Ap5A) on the 22S dynein ATPase was also investigated. Ap5A acted as a weak competitive inhibitor of the ciliary 22S dynein ATPase and the nonlinearity of the double-reciprocal plot of the ATPase was confirmed in the presence of Ap5A.