Structural Characterization of Two δ Chain Variants

Abstract

Hemoglobin Flatbush, from two Negro families, is characterized by the substitution of a glutamyl residue for the alany1 residue in position 22 of the 6 chain.The resulting abnormal tryptic peptide, 6T-3, is thus identical with the corresponding /3 chain geptide.The possible evolutionary significance of this relationship is discussed.Further evidence is presented that Hemoglobin A'2 (Bz) obtained from three different sources is characterized by the substitution of an arginyl residue for the glycyl residue in position 16 of the 6 chain.The amino acid compositions of all the other tryptic peptides from these two variant hemoglobins were normal.Three inherited variants of 1luma.nhemoglobin A2 (Hb AZ) are known which differ in clectrophorctic mobility from one another and from normal Hb A,.Each variant appears to result from a single amino acid substitution.One of these, Hb Sphakia, found in three members of a family in Crete, was shown to havr an arginyl residue substitutA,d for thr: histidyl residue in position 2 of the 6 chain, or a2622 *lg (I).A second hemoglobin, Hb b'z (also known as B2), which occurs in about 1 010 of the Negro population of the Southeastern United States, is characterized by the substitution of an srginyl r&duo for the glycinc in position 16 of the 6 chain; i.e.CU&,~ Arg.Stretton (2) waq the first to point out the probability of this structure.Confirmation of this substitution was presented by Jones, Boerma, and Huisman at the Seattle meeting of the American Society of Human Genetics in 1965 (3).Rcccntly and independently, Ball et al. (4) cstended the studies of Stretton to the