Interpretation of the low angle X-ray diffraction from insect flight muscle in rigor

Abstract

The structure of insect flight muscle is formally described in terms of actin-based cross-bridges upon which successive symmetry operations are performed, in combination with a modulation function. The Fourier transform of the structure is generated by means of these steps. The model transform is fitted to the observed diffraction pattern from insect flight muscle in rigor and the position of the rigor cross-bridges deduced; they are found to lie across the long helix of actin monomers and to project away from the thin filament. The cross-bridges interact with approximately one-third of the actin monomers, and show a strong preference for a particular orientation between the thick and thin filaments.