Figure 9.

Measuring F₁-ATPase power stroke angular velocity vs. rotary position from red light intensity of a rotating AuNR collected at 200 kHz (200,000 fps). (A). Example of changes in scattered light intensity vs. time during an EcF₁ power stroke in saturating 1 mM Mg-ATP. This power stroke occurred subsequent to the catalytic dwell, which had been set to a minimum light intensity by rotating the polarizer prior to data collection. Power stroke rotational position vs. time was calculated from scattered light intensity using Eq. 1 (red) and Eq. 2 (blue). (B). Average power stroke angular velocity vs. rotational position of EcF₁ ATPase-driven γ-subunit rotation binned for every 3° of rotation from the end of the catalytic dwell, which was designated as 0° in the presence of saturating 1 mM Mg-ATP (black) and 0.3 mM Mg-ATP (red). Inset: Distribution of ATP-binding dwells vs. rotational position in the presence of 0.3 mM Mg-ATP, which is proportional to the decrease in average angular velocity vs. rotational position at 0.3 mM Mg-ATP. (C). Distributions of ADP-binding dwells (red) and ADP-dependent velocity decreases (green) vs. rotational position of the power stroke at 1.0 mM MgATP and 3 mM MgADP. (D). Activation energy of the EcF₁-ATPase power stroke vs. rotational position at 1 mM Mg-ATP, 10 μM Mg-ADP and 10 μM Pi. Energy stored vs. extent of twist of a torsion spring with spring constants, κ = 50 k_BT rad⁻² (red) and κ = 150 k_BT rad⁻² (green) from equilibrium positions of 34° and 93°, respectively. Inset: Distribution of ATP-binding dwells vs. rotational position from B. This figure was reconfigured using data from Martin et al. (2014, 2018), Sielaff et al. (2016).