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232 PART` III. ABNORMAL HEMOGLOBINS aspartic or glutamic acid residues or a greater number of carboxyl groups existing as amides or esters than is true of the normal protein. Possible Bases for Differences in Content of Free Carboxyl Groups in Hemoglobins A, S and C. Per molecule of hemoglobins S and C in comparison with hemoglobin A, one or more of the following possibilities should account for the differences: 1) Smaller number of aspartic and/or glutamic acid residues; 2) Larger number of terminal and/or aspartic and/or glutamic car- boxyl groups existing as amides; 3 ~ Larger number of esterified terminal and/or aspartic and/or glutam- ~c carboxyl groups. REFEREN CES 1. Pauling, L., Itano, H. A., Singer, S. J., and Wells, I. C.: Sickle cell anemia a molecular disease, Science, 110: 543-548, 1949. 2. Itano, H. A., and Neel, J. V.: A new inherited abnormality of human hemoglobin, Proc. Nat. Acad. Sci., 36: 613-617, 19 50. 3. Perutz, M. F`., Liquori, A. M., and Eirich, F.: X-ray and solubility studies of the hemoglobin of sickle cell anemia patients, Nature, 167: 929-931, 1951. 4. Cohn, E. J., and Edsall, l. T.: Proteins, amino acids and peptides, Chapter 20: 440505, Monograph Series No. 90, Reinhold Publishing Corp., New York, 1943. 5. Scatchard, G., and Black, E. S.: The effect of salts on the isotonic and isoelectric points of proteins, J. Phys. & Colloid Chem., 53: 88-99, 1949. 6. Havinga, E.: Comparison of the phosphorus content, optical rotation, separation of hemes and globin, and terminal amino-acid residues of normal adult human hemoglobin and sickle cell anemia hemoglobin, Proc. Nat. Acad. Sci., 39: 59-64, 1953. 7. Scheinberg, I. H., Harris, R. S., and Spitzer, J. L.: Diderential titration by means of paper electrophoresis and the structure of human hemoglobins, Proc. Nat. Acad. Sci., 40: 773-783, 1954. DISCUSSION Dr. R. Benesch: I would like to make one comment on Dr. Scheinberg's paper. He said that charge contributions from RS- in determining the elec- trophoretic mobility of proteins could only be expected at pH 11 or above. N/Yhile this would be true for tyrosine, it would not be true for -STI because, while we do not know the exact pK in hemoglobin, it is certainly a lot lower, semewhere around 9.