Effects of N-Ethylmaleimide on Dynein Adenosinetriphosphatase Activity and Its Recombining Ability with Outer Fibers

The effects of N-ethylmaleimide (NEM) on ciliary ATPase (dyneins) [EC 3.6.1.3] of Tetrahymena pyriformis were investigated. Like muscle myosin ATPase, 30 S dynein ATPase was activated biphasically by NEM, while 14 S dynein ATPase was simply inhibited. The maximal activation of 30 S dynein ATPase was obtained by preincubation with NEM at a concentration of 50 μM (0.23 μmole NEM/mg protein) and the magnitude of activation was 2.5- to 3-fold. The changes in the characteristics of 30 S dynein ATPase caused by modification were studied in comparison with those of myosin ATPase. It was confirmed that 30 S dynein ATPase was a myosin-like enzyme, though a few differences were found. From recombination tests of modified 30 S dynein with outer fibers, it was shown that at least three types of -SH groups are present in 30 S dynein molecules; -SH groups responsible for recombination with outer fibers, for enhancement of the enzyme activity by their blockage, and for catalytic activity.