Rotation of the ε subunit in F1-ATPase from thermophilic Bacillus strain PS3 (TF1) was observed under a fluorescence microscope by the method used for observation of the γ subunit rotation (Noji, H., Yasuda, R., Yoshida, M., and Kinosita, K., Jr. (1997) Nature 386, 299-302). The α3β3γε complex of TF1 was fixed to a solid surface, and fluorescently labeled actin filament was attached to the ε subunit through biotin- streptavidin. In the presence of ATP, the filament attached to ε subunit rotated in a unidirection. The direction of the rotation was the same as that observed for the γ subunit. The rotational velocity was slightly slower than the filament attached to the γ subunit, probably due to the experimental setup used. Thus, as suggested from biochemical studies (Aggeler, R., Ogilvie, I., and Capaldi, R. A. (1997) J. Biol. Chem. 272, 19621-19624), the ε subunit rotates with the γ subunit in F1-ATPase during catalysis.
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