Figure 6.

Power stroke. Sequential mix single-turnover experiments were performed in which 0.25 μm MV FlAsH.QSY-CaM was mixed with ATP (0.2 μm), aged for 10 s, and then mixed with different concentrations of actin. A, the increase in FRET was monitored by the decrease in FlAsH fluorescence and was best fit by a three-exponential function. B, the fast phase of the fluorescence transients (fast power stroke) was plotted as a function of actin concentration and fit to a hyperbolic or linear function. C, the slow phase (slow power stroke) was hyperbolically dependent on actin concentration, whereas the very slow fluorescence increase was similar at all actin concentrations. Fluorescence is reported in arbitrary units (AU).