Fig. 2.
IXa-MD binds to actin filaments in the absence and presence of nucleotide. (A) The fractions of actin-bound IXa-MD versus actin concentration were obtained from cosedimentation assays using IXa-MD and increasing actin concentrations in the absence or presence of nucleotide (Materials and Methods). Mean values ± SD from three experiments in each condition are shown; the concentration of IX-MD used was between 0.2 and 0.5 μM, dependent on the preparation. (B) The fractions of actin-bound IXa-MD versus actin concentration were obtained from cosedimentation assays in the absence or presence of calcium. Mean values ± SD from three experiments in each condition are shown. (C) The affinities obtained from the experiments in A and B are summarized in the table, with the Kd dissociation constant and Fmax fraction of myosin bound to F-actin.