Stimulation of F₁-ATPase activity by sodium dodecyl sulfate

F₁-ATPase is a rotary molecular motor in which the γ subunit rotates inside the cylinder made of α₃Β₃ subunits. We have studied the effects of sodium dodecyl sulfate (SDS) on the rotational and ATP hydrolysis activities of F₁-ATPase. Bulk hydrolysis activity at various SDS concentrations was examined at 2mM ATP. Maximal stimulation was obtained at 0.003% (w/v) SDS, the initial (least inhibited) activity being about 1.4 times and the steady-state activity 3-4 times the values in the absence of SDS. Rotation rates observed with a 40-nm gold bead or a 0.29-μm bead duplex as well as the torque were unaffected by the presence of 0.003% SDS. The fraction of beads that rotated, in contrast, tended to increase in the presence of SDS. SDS seems to bring inactive F₁ molecules into an active form but it does not alter or enhance the function of already active F₁ molecules significantly.