SPECIFICITY IX SICKLE CELL HEMOGLOBIN MOLECULES 169 



shape and rigidity, sickled cells tend to block off small blood vessels and cause 

 tissue destruction. The spleen is a common site of occurrence of this phenom- 

 enon in sickle cell anemia. The amount of intravascular sickling in sickle cell 

 hemoglobin C disease is small, and the incidence of splenic infarction under 

 normal conditions is low. Several instances of splenic infarction in sickle cell 

 hemoglobin C disease have been observed in previously well subjects at alti- 

 tudes of 4000-6000 feet in unpressurized airplanes. In sickle cell trait splenic 

 infarctions have occurred only at higher altitudes of 10,000-15,000 feet. 



The discovery that the hemoglobin in sickling cells has abnormal electro- 

 phoretic behavior suggested further investigation of its physical properties. 

 Gellation and solubility studies showed differences in the interactions of hemo- 

 globin S and the other abnormal hemoglobins. In gellation studies the behavior 

 of concentrated hemoglobin solutions prepared by the lysis of red blood cells 

 was examined. These solutions contain other soluble constituents of the red 

 cell and are relatively low in salt concentration. It was discovered by Harris 

 (1950) that if a solution of oxyhemoglobin S of greater than 10 per cent con- 

 centration were deoxygenated, a rise in viscosity occurred; below 10 per cent 

 concentration no change in viscosity occurred. The viscous solutions prepared 

 in this manner contain birefringent, spindle-shaped aggregates of hemoglobin 

 S. Harris also observed that solutions of higher concentration became gels 

 when deoxygenated. By testing progressive dilutions of concentrated mixtures 

 containing hemoglobin S, Singer and Singer (1953) determined the minimum 

 concentration at which gellation occurs. For the S-F mixtures of sickle cell 

 anemia the minimum concentration for gelling was 19-25 per cent. The mini- 

 mum concentrations for the A-S mixtures of sickle cell trait and the S-C mix- 

 tures of sickle cell hemoglobin C disease were 30-33 and 26-28 per cent, re- 

 spectively. In terms of the hemoglobin S concentration at least 19 per cent was 

 required to cause sickle cell anemia samples to gel. In sickle cell trait and sickle 

 cell hemoglobin C disease the minimum hemoglobin S concentrations for gel 

 formation were 10-16 and 9-13 per cent, respectively. Thus, although hemo- 

 globins A and C do not form gels in the absence of hemoglobin S, they can take 

 part in gel formation in the presence of S and reduce the concentration of S 

 required for gellation to occur. 



The determination of hemoglobin solubility in concentrated salt solutions 

 provides a quantitative measure of interactions in mixtures and is more readily 

 controlled than sickling or gellation studies. Landsteiner and Heidelberger 

 (1923) compared solubilities of the oxyhemoglobins of different mammals. 

 They found that the solubilities of mixtures prepared from different species 

 had additive solubilities but that a mixture of donkey and horse hemoglobins 

 interacted to yield an intermediate solubility. Kunitz and Northrop (1938) 

 studied the solubility behavior of protein mixtures in salt solutions and applied 

 the phase rule to the interpretation of their data. In a typical experiment in- 



