Differences in the Amino Acid Sequences of Tryptic Peptides from Three Sheep Hemoglobin β Chains

Tryptic peptides were isolated from the β chains of sheep hemoglobins A, B, and C and placed in linear array through the use of nonuniform radioactive label. Nearly complete sequence analysis indicates that the β chains of hemoglobins A and B contain 145 amino acids while the β chain of hemoglobin C lacks 4 residues in its NH2-terminal portion and contains only 141 amino acids. The sum of differences between the sequences of A and B β chains involves a minimum of 7 residues, the sum between A and C, a minimum of 16 residues, and the sum between B and C a minimum of 21 residues. The β chains of A and C share a common difference with respect to the β chain of B at five sites. It is likely that one or more of these five differences account for the increased oxygen affinity which hemoglobins A and C share when compared with hemoglobin B.