Introductory Remarks at the Beginning of Session IV
A great deal is now known about the structure of the sickle cell hemoglobin precipitate. In 1950 Murdoch Mitchison and I found that sickle cells are birefringent and show polarization dichroism. From the sign of the birefringence we were able to conclude that the hemes lie approximately perpendicular to the long axis of the sickled cells. It took over 20 years before further information emerged about the structure of the crystalline precipitate in the red cell. Recently Dr. J. Bertles in St. Luke1s Hospital in New York got marvelous electron micrographs of sickle cells and of ultra centrifuge pellets of deoxyhemoglobin S precipitates. These pictures show fibers of 150 to 170 Å diameter and roughly square packing running all along the length of the cell. Dr. B. Fairchild and Dr. Swerdlow took x-ray fiber diffraction of deoxyhemoglobin S and obtained a rich diffraction pattern from which something about the arrangement of hemoglobin molecules in the fiber can be deduced. They suggest that the fibers are helical, with 11 or 13 molecules in two turns of helix, and a helix repeat of 64 Å per turn. This would be consistent with Mitchinson and my own results if the molecular twofold axis lay normal to the fibre axis, and the long axis (65 Å) of the molecule lay roughly parallel to the fibre axis.
KeywordsSickle Cell Fibre Axis Single Amino Acid Substitution Intermolecular Contact Introductory Remark
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