Spin label mobilities. (A) CW EPR spectra of single-Cys mutants in three biochemical states. (B) Order parameter of IPSL from the spectra in A, in biochemical states apo (prehydrolysis, black), ADP.V (posthydrolysis, green), and actin-bound (red). (C) Order parameter from MD trajectories based on crystal structures 1FMV (postrigor, black), 1VOM (pre-powerstroke, green), and 1W8J (rigor-like, red).