X-ray equatorial diffraction studies on the cross-sectional structure of Salmonella flagella

X-ray diffraction studies have been made on the cross-sectional structure of the normal Salmonella flagella. Two approaches have been made: one based upon small-angle equatorial scatterings (2θ 3°) and the other upon moderate-angle angle equatorial diffractions (3° 2θ 10°).Analysis of small-angle scattering data gives the radius of gyration of the flagella as 68 Å. Cylindrically averaged electron density of the cross-section of the flagella is obtained by means of the Fourier-Bessel transformation method. The average radius of the flagella is about 65 Å.In the investigation of the moderate-angle diffraction pattern, validity is examined of the model that a flagellum consits annularly arranged strands, of which each has a cylindrically symmetric structure. Features of the pattern observed in the range of 3° < 2θ < 10° can be interpreted fairly well by this model. Average radii of the flagella obtained for the 11 and 13 strands models are close to that obtained by the analysis of the small-angle scattering data.