Direct determination of crystallographic phases for diffraction data from phospholipid multilamellar arrays.

Direct determination of crystallographic phases based on probabilistic of sigma 1 and sigma 2 "triplet" structure invariants has been found to be an effective technique for structure analysis with lamellar x-ray or electron diffraction intensity data from phospholipids. In many cases, nearly all phase values are determined, permitting a structure density (electron density for x-ray diffraction; electrostatic potential for electron diffraction) map to be calculated, which is directly interpretable in terms of known bilayer lipid structure. The major source of error is found to be due to the distortion of observed electron diffraction intensity data by incoherent multiple scattering, which can significantly affect the appearance of the electrostatic potential map, but not the success of the phase determination, as long as the observed Patterson function can be interpreted.