The amino acid sequence of a major polypeptide chain of earthworm hemoglobin

The amino acid sequence has been determined for polypeptide chain AIII of the major component of the hemoglobin (erythrocruorin) from the earthworm, Lumbricus terrestris. The chain has 157 residues and a molecular weight of 17,496. Although the extent of sequence identity with other globin chains is only 17-18%, analysis of the sequence leads to the conclusion that the secondary structure of the chain is very similar to those of vertebrate globins and that about 60-70% of the amino acid residues are in alpha helices. The D helix appears to be missing, as it is from the alpha chain of human hemoglobin and from the monomeric hemoglobin of Glycera dibranchiata, another annelid worm. This is the first sequence obtained from one of the "giant" extracellular hemoglobins of invertebrate animals.