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.
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