Fig. 10.

Time-resolved negative staining showing the msec time-course of head reordering on scallop thick filaments following Ca²⁺ removal. Each panel shows a field of negatively stained scallop thick filaments, an oscilloscope trace (left inset) showing time in activating (high Ca²⁺) and/or relaxing rinse (low Ca²⁺), and an averaged Fourier transform of 20 representative filaments at right (numbers indicate spacing of main helical repeat (∼ 48 nm) and axial spacing of head crowns (∼14.5 nm); the presence of layer lines indicates helical ordering of the myosin heads). (a) relaxed control: grid rinsed for 70 msec with relaxing rinse, then stained – myosin heads are ordered; (b) activated control: 30 msec activating rinse then stained – heads disordered; (c) 20 msec reversal: 30 msec activating rinse, 20 msec reversing rinse, then stained – heads partially reordered; (d) 30 msec reversal: 60 msec activating rinse, 30 msec reversing rinse, then stained – heads more reordered; (e) 50 msec reversal: 60 msec activating rinse, 50 msec reversing rinse, then stained – heads fully reordered. (From Zhao and Craig, 2003).