The structure of sheep hemoglobins: II. The amino acid composition of the tryptic peptides of the non-α chains of hemoglobins A, B, C, and F

Abstract

This paper contains detailed data of the amino acid compositions of the peptides from tryptic digests of the non-α chains of the three adult sheep hemoglobins A, B, and C and of sheep fetal hemoglobin. Sequential arrangements of amino acids of some of these peptides are also presented. The peptides were isolated from 2- and 24-hour tryptic digests by Dowex-50 chromatography and purified on Dowex-1 resin. The β chains of the adult hemoglobins A and B and the γ chains of fetal hemoglobin contain likely 145 residues with methionine in amino terminal position. The minimal number of differences between the two adult chains is 6; these differences include a methionine residue in position 76 and a proline residue in position 58. The β chain of hemoglobin C, which replaces the β chain of hemoglobin A in sheep homozygous for hemoglobin A during severe anemia, may contain 141 residues with proline in amino terminal position. Excluding the first 8 residues from the comparison, at least 12 differences are likely to exist between the β chains of the hemoglobins A and C. The γ chain differs from the β chain of hemoglobin B minimally in 27 residues. A comparison of the putative structures of these chains with the corresponding bovine polypeptide chains revealed a greater resemblance than noted with any other non-α chain from species studied. Since the structural differences between the non-α chains of the hemoglobins A, B, and C are located in various positions in the total chain structures, it seems indicated (a) that the allelic genes governing the structural synthesis of the β chains of the hemoglobins A and B are greatly different in structure, and (b) that the synthesis of the β chain of hemoglobin C is controlled by a structurally different and “silent” gene, which is activated during severe anemia.