Low-angle x-ray diffraction and electronmicroscope studies of isolated erythrocyte membranes.

Two alternative sequences of low angle X-ray diffraction patterns (Type I and Type II) have been observed during the controlled dehydration of rat (and human) erythrocyte ghost preparations in which the residual haemoglobin content has varied. The Type I sequence has been obtained when haemoglobin has comprised more than 30 % of the total protein of the membrane preparation. It features an initial lamellar pattern that has been interpreted in terms of a predominantly continuous lipoprotein sandwich structure. Subsequent changes in diffraction pattern have been suggested to represent a partial breakdown of the lipoprotein structure to give a multiphase system. The Type II sequence was most readily obtained from haemoglobin-free ghosts. At no stage during the dehydration of these ghosts did the diffraction feature a stable lamellar pattern. At all levels of hydration the X-ray reflections appeared to represent independent lipid and lipoprotein phases. Osmium tetroxide fixation of haemoglobin-free membranes prevented the separation of lipid and lipoprotein phases during dehydration. Comparisons of electron micrographs of condensed membrane preparations have revealed some structural differences between membranes which give rise to the Type I and Type II diffraction sequences.