Amino acid composition of hemoglobins of normal Negroes and sickle-cell anemics

Abstract

The recent electrophoretic experiments of Pauling, Itano, Singer, and Wells (1) have demonstrated that the hemoglobins of normal Negroes and of sickle-cell anemics are unlike; in a buffer of suitable pH the two components of a mixture of these hemoglobins migrate in opposite directions. On the basis of the difference in their isoelectric points, it was concluded that the hemoglobin of sickle-cell anemics has 2 to 4 more net positive charges per molecule than normal hemoglobin. There is evidence that the composition of the heme moiety is the same in both proteins; one hypothesis which has been advanced to explain the dissimilarity of the two hemoglobins assumes a difference in the number or kind of ionizable groups in the molecules, that is, in the acidic or basic amino acids of the globin. Thus, the observed difference in charge might result from a small decrease in the number of acidic amino acids or a small increase in the number of basic amino acids in the molecule of sickle-cell hemoglobin relative to that of normal hemoglobin or from relatively large alterations in amino acid content in which the charges were almost compensated. The object of the present study was to determine the amino acid composition of the two hemoglobins in order to ascertain the validity of this hypothesis. The analysis was made by means of the methods of starch chromatography which have recently been developed by Moore and Stein (2-6). The hydrolysates of two independently prepared samples of normal carbonmonoxyhemoglobin (to be referred to as N-Hb) and one sample of sickle-cell anemia hemoglobin (SC-Hb) have been analyzed. Approximately ten to fifteen individual determinations of each of seventeen amino acids and ammonia have been made by means of about 70 starch chromatograms.

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