Analysis of equatorial x-ray diffraction patterns from muscle fibers: factors that affect the intensities

Previously we have shown that cross-bridge attachment to actin and the radial position of the myosin heads surrounding the thick filament backbone affect the equatorial x-ray diffraction intensities in different ways (Yu, 1989). In the present study, other factors frequently encountered experimentally are analyzed by a simple model of the filament lattice. It is shown that the ordering/disordering of filaments, lattice spacing changes, the azimuthal redistributions of cross-bridges, and variations in the ordered/disordered population of cross-bridges surrounding the thick filaments can distinctly affect the equatorial intensities. Consideration of Fourier transforms of individual components of the unit cell can provide qualitative explanations for the equatorial intensity changes. Criteria are suggested that can be used to distinguish the influence of some factors from others.