Intermolecular Organization of Deoxygenated Sickle Haemoglobin determined by X-ray Diffraction

Abstract

SICKLE cell haemoglobin (haemoglobin S), which presumably arises from a single mutation at the β-chain locus, differs from normal adult haemoglobin (haemoglobin A) by a replacement of valine for glutamic acid in the sixth position of both β-chains of the haemoglobin molecule¹. It has long been known that sickle cell anaemia erythrocytes containing deoxygenated haemoglobin S are birefringent between crossed nicol prisms^2,3, and that the mean plane of the porphyrin rings is approximately perpendicular to the long axis of these sickled cells². Erythrocytes containing haemoglobin A or oxygenated haemoglobin S are not birefringent. Aggregation of deoxygenated haemoglobin S, responsible for birefringence, is the basic mechanism of the sickling phenomenon. The only structural information on the aggregates has been obtained through direct observations with the electron microscope. These have revealed that deoxygenated haemoglobin S molecules in sickled cells^4–6 and in cell-free solutions⁷ lying in parallel arrays form rod-like structures with a diameter ranging from 140 Å to 170 Å.