Mohammad Delawar Hossain^{a, b}, Shou Furuike^a, Yasuhiro Onoue^{a, c}, Kengo Adachi^a, Masasuke Yoshida^{d, e} and Kazuhiko Kinosita Jr.^{a, *}

^a Department of Physics, Faculty of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
^b Department of Physics, School of Physical Sciences, Shahjalal University of Science and Technology, Sylhet-3114, Bangladesh
^c Department of Functional Molecular Science, The Graduate University for Advanced Studies (Sokendai), Okazaki, Aichi 444-8585, Japan
^d Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta 4259, Yokohama 226-8503, Japan
^e ATP-Synthesis Regulation Project, International Cooperative Research Project (ICORP), Japan Science and Technology Agency (JST), Aomi 2-41, Tokyo 135-0064, Japan

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 2 mM 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.

Keywords: Single molecule; Optical microscopy; Detergent; Torque; ATP synthase; ATP hydrolysis