Complete amino acid sequences of the major early embryonic alpha-like globins of the chicken.

Vertebrate embryos contain hemoglobins composed of globin polypeptides structurally distinct from those of adults. Together with fetal and adult globin chains, these early embryonic globins are encoded by two developmentally regulated multigene families. To facilitate analysis of the structure and evolution of early embryonic alpha-globin genes, we have determined the complete amino acid sequences of the pi and pi' alpha-like globins of the chick embryo. While differing from each other by an alanine/glutamic acid interchange at position 124, this pair of sequences differs from the major and minor adult alpha-globins by 43%. The early embryonic and adult alpha-like sequences appear to have diverged following an ancient gene duplication. We discuss specific amino acid substitutions in functional positions as possible mediators of the reduced Bohr effect and elevated oxygen affinity, which are characteristic of early embryonic hemoglobins.