The determination of the first-order phase in membrane diffraction using electron density strip models

The problem of assigning the phase to the first-order reflection in membrane diffraction is treated. Biological membrane assemblies with two membranes per unit cell and the special case of lipid bilayers are treated. Phase assignment is dependent on the origin value of the minus fluid or the minus lipid model and on the actual asymmetry of the membranes. The conditions for phase assignment are derived from a study of single- and three-strip electron density models.