Differences in the amino acid sequences of tryptic peptides from three sheep hemoglobin beta chains.

Tryptic peptides were isolated from the ,8 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 /3 chains of hemoglobins A and B contain 145 amino acids while the p chain of hemoglobin C lacks 4 residues in its NH&erminal portion and contains only 141 amino acids. The sum of differences between the sequences of A and B /3 chains involves a minimum of 7 residues, the sum betweenA and C, aminimum of 16 residues, and the sum between B and C a minimum of 21 residues. The /3 chains of A and C share a common difference with respect to the @ 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.