FIGURE 2.

Stepping rotation of βGlu-190 mutants. a, examples of the time course of rotation by F₁(βE190A). Buffer was exchanged during observation, and ATP concentration was reduced from 100 μm (red) to 50 nm (blue). The insets are x-y trajectories during rotation in the presence of 100 μm (left) or 50 nm ATP (right). b, histogram of the angular position of F₁(βE190A) in the presence of 100 μm (bottom) or 50 nm ATP (top). Δθ₁ and Δθ₂ represent the angle distances of the pausing angles at 50 nm ATP compared with those at 100 μm ATP. c, distributions of angle distances of F₁(βE190A) (Δθ₁ and Δθ₂). The average values of Δθ₁ and Δθ₂ are −1.8 ± 6.4 and 33 ± 9.2° (mean ± S.D., n = 33). d, examples of the time course of rotation by F₁(βE190Q). Buffer was exchanged during observation, and ATP concentration was reduced from 10 μm (red) to 10 nm (blue). e, histogram of the angular position of F₁(βE190Q) in the presence of 1 mm (bottom) or 1 nm ATP (top). Δθ₁ and Δθ₂ represent the angle distances of the pausing angles at 1 nm ATP from that at 1 mm ATP. f, distributions of angle distances of F₁(βE190Q) (Δθ₁ and Δθ₂). The average values of Δθ₁ and Δθ₂ are 9.9 ± 10 and 54 ± 12° (mean ± S.D., n = 21).