John Barrington Leigh

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

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.

The effect of disorientation on the intensity distribution of non-crystalline fibres. I. Theory

The intensity function in reciprocal space is derived for the case of non-crystalline fibres with a Gaussian distribution of orientations. An expression is found relating the observed intensity function with the weighted integral along a circle of the intensity derived from the molecular structure factor. From this result in the case where the layer-line width is very small a correction factor may be derived which, if applied to the observed intensity, yields the intensity which would be obtained from a perfectly orientated fibre. The general problem of correcting for disorientation can only be treated by a numerical deconvolution procedure.