Aggregated forms of deoxyhemoglobin S were examined with a field emission transmission electron microscope. Images of isolated helical fibers were obtained from sickled cell lysates stained directly on the electron microscope grid. Optical and digital analyses of the electron micrographs showed that the fibers are similar to those characterized by J. T. Finch, M. F. Perutz, J. F. Bertles, and J. Dobler [(1973) Proc. NatL Acad. Sci. USA 70, 718-7221 in that they consist of stacked discs each composed of six hemoglobin molecules. The fibers exhibit an outer diameter of 160-170 A and an inner diameter of about 60 A with an axial spacing of 58 A per disc. The fiber can be described as a helix consisting of 56 discs per helical turn. We observed discs of six hemoglobin molecules, which may be stable substructural components of the fibers. They were observed in preparations of hemoglobin fibers and exhibited 6-fold symmetry by power spectrum analysis. A reconstructed image of a disc digitally filtered for 6-fold symmetry has a maximum external diameter of -170 A and a central hole of 60 A diameter and is similar to the axial projection of a single disc from a low-resolution, three-dimensional reconstructed model of a fiber.The erythrocyte sickling phenomenon of sickle cell anemia is associated with aggregation of hemoglobin S (HbS) molecules into linear arrays or fibers (1-9). These aggregates form long bundles of fibers within the erythrocyte and are believed to be responsible for deformation of the cell into abnormal shapes with the consequent acute physiologic manifestations known as sickle cell crisis. The molecular basis of sickle cell anemia is a mutation in the 13-globin gene causing replacement of Glu A3(6)# with valine in each of the subunits of hemoglobin (11).It is clearly desirable to relate the structural alteration of the hemoglobin molecule to the mechanism responsible for the formation of the characteristic linear aggregates. Structural features of aggregates of deoxyhemoglobin S (deoxyHbS) molecules have been characterized by electron microscopy (1-5), x-ray diffraction (6), and physical chemical studies (7)(8)(9)(10). On the basis of these studies, models have been presented that are consistent with the fl6 site at the points of intermolecular contact (12); however, direct structural determination of the molecular orientation of the deoxyHbS molecule in the fiber is required to resolve the role of the substituted valine residue.Correlating the features of the fibers with the chemical and physical properties of the deoxyHbS molecule has been complicated by the fact that at least two distinct types of fibers have been described by electron microscope studies: a six-stranded helix (1, 2) having 6-fold axial symmetry and two types ofThe costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. eight-stranded helices in which pairs of st...

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