SPECIFICITY IX SICKLE CELL HEMOGLOBIN MOLECULES 167 



mobility of hemoglobin S and solubility of hemoglobin A (Itano, 1951). A 

 number of other abnormal hemoglobins have been found with use of the electro- 

 phoretic method; however, hemoglobins C and D are the only abnormal forms 

 known to be associated with sickle cell disease. 



It seems reasonable to assume that the ultimate origin of the abnormal 

 hemoglobins were mutations in the gene which determines the structure of 

 hemoglobin A. The mutations resulted in changes in amino acid sequence or 

 composition, or both; and these changes produced the alterations in net charge 

 and surface configuration manifested by abnormalities in electrophoretic 

 mobilities and solubilities. The alterations were not sufficient to alter the 

 ability of the abnormal hemoglobins to combine reversibly with oxygen since 

 each of the known forms functions as an oxygen carrier in blood. 



In this paper I shall discuss the ways in which the aggregating property of 

 hemoglobin S has been observed and measured. The sickling behavior of red 

 cells was studied long before the discovery that an abnormal hemoglobin occurs 

 in sickle cell anemia. It was known that the removal of oxygen causes sickling 

 in the cells of certain individuals (Hahn and Gillespie, 1927) and that the ease 

 with which sickling could be induced varies in different individuals (Emmel, 

 1917). In those whose sickling cells are not accompanied by anemia, sickling 

 occurs more slowly than in those with anemia. Even among those who have 

 anemia with sickling cells, some have cells which sickle less readily than in the 

 usual case of sickle cell anemia (Cooke and Mack, 1934). Moreover, there is a 

 difference in the shape of the sickled cells from anemic and non-anemic indi- 

 viduals. In sickle cell anemia the typical sickled cells have the shape of slender, 

 elongated crescents and spindles with filamentous extensions from each end. 

 In the non-anemic carriers of the sickle cell trait the cells assume a more com- 

 pact and multi-pointed form, and the filaments are not as prominent. The two 

 types of sickling are called "filamentous" and "holly-leaf", respectively (Neel, 

 1951). Sickled cells are rigid (Murphy and Shapiro, 1944) and are birefringent 

 (Sherman, 1940); in contrast, oxygenated cells containing sickle cell hemoglobin 

 and normal cells, oxygenated or deoxygenated, are flexible and show no sign 

 of hemoglobin aggregation or orientation. The cells in sickle cell trait do not 

 sickle at the oxygen tension of venous blood; whereas in sickle cell anemia a 

 high proportion of the cells in venous blood are partially or completely sickled 

 (Sherman, 1940). When sickle cell anemia subjects are placed in an atmosphere 

 with a high partial pressure of oxygen, the percentage of sickled cells in their 

 blood and the rate of destruction of their red blood cells in the circulation 

 diminish (Reinhard, et al, 1944; Callender, et al., 1949). Genetically, sickle cell 

 anemia is due to homozygosity in the sickle cell gene (Neel, 1949). Normal 

 adult hemoglobin is absent, and hemoglobin S is the only abnormal hemoglobin 

 present. As in other chronic anemias, fetal hemoglobin may also be present. 

 Sickle cell trait is due to the presence of one allele each for sickle cell hemoglobin 



