Table 1.

Comparison of event durations obtained from fluorophore polarization, laser trap displacement, and biochemical rate constants

[MgATP]	Event durations, ms
	10 μM	1 μM
Fluorophore polarization	187  ±  14 (n = 15)	376  ±  30 (n = 13)
Laser trap unitary displacements*	158  ±  19 (n = 12)	505  ±  77 (n = 6)
Biochemical model†	≈120	≈570

^*Estimates of event durations obtained by mean-variance analysis of single myosin molecule displacement records in the laser optical trap (see ref. 20 for details) under identical ionic and experimental conditions used in the fluorescence polarization experiments. 

^†Using rate constants from solution studies of the actomyosin ATPase cycle (28), for MgADP release (≈15 s⁻¹) and for MgATP binding and subsequent myosin detachment from actin (≈2 × 10⁶ M⁻¹ s⁻¹), one can calculate the total time associated with MgADP release, MgATP binding, and myosin detachment, i.e., presumably the duration of the powerstroke.