Studies on the Adenosine Triphosphatase Activity of 14 S and 30 S Dynein from Cilia of Tetrahymena

The axonemal adenosine triphosphatase protein, dynein, consists of 14 S and 30 S fractions. Both forms of dynein require the presence of a divalent cation for activity: Mg++, Ca++, Mn++, Fe++, Co++, and Ni++ can all function as activator, but Be++, Cd++, Sr++, and Zn++ cannot. Specificity for ATP or deoxy-ATP is moderately high; other nucleoside triphosphates are hydrolyzed at only about 10% of the rate of ATP; AMP, pyrophosphate, and p-nitrophenyl phosphate are not hydrolyzed. The two forms of dynein both have a pH optimum at pH 8.5 to 9.0. Addition of neutral salts to the assay medium inhibits the activity of 14 S dynein but enhances that of 30 S dynein. When assayed under standard conditions with Mg++ activation, 14 S and 30 S dynein had maximal velocities of 3.5 and 1.3 µmoles of Pi per (min x mg of protein), respectively, and Michaelis constants of 3.5 x 10-5 and 1.1 x 10-5 m. The general similarity in enzymatic properties is consistent with a monomer-polymer relationship between 14 S and 30 S dynein, with the differences that occur being the results of a configurational change attendant upon polymerization. The possible physiological significance of the partial repression of ATPase activity in 30 S dynein is discussed.