Fig. 1.

Oscillation of F₁ torque probed using magnetic tweezers. (A) Experimental design (not to scale). Rotation of magnetic beads attached to F₁ is manipulated with magnetic tweezers. (B) (Upper) Angular displacement of trapped beads in the presence of F₁ torque. θ_TC indicates an angular position at which magnetic beads are trapped under a certain magnetic field in the absence of F₁ torque (τ_F1). In the presence of τ_F1, the bead angle shifts to θ_B so that τ_F1 and magnetic torque (τ_M) are balanced. (Lower) Positional relationship between γ, bead, and magnetic trap center at time t during manipulation. S_γB represents external elastic component that cause the shift of θ_B from θ_γ (for the definition and estimation see Methods, Torque Profile As a Function of θ_γ). S_BM is the putative spring by magnetic trap. Its magnitude of torque is defined with Eq. 1. (C) Example trace of F₁ torque as a function of θ_TC. Raw data points during controlled rotation (0.04 Hz, ATP hydrolysis direction) are shown in red. Black shows a result of 200-point median filtering. The substrate concentrations are 10 μM (ATP), 10 μM (ADP), and 100 μM (P_i) (condition i in Fig. 2C). (D) Magnified plot. Torque jumps are indicated by arrowheads.