Structure of the polypeptide chain of extracellular hemoglobin from the nematode Ascaris suum.

1. Ascaris suum extracellular hemoglobin is composed of eight identical single polypeptide chain subunits carrying two heme binding sites each. 2. Limited trypsinolysis followed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis gave a major band corresponding to half the molecular mass of an intact subunit. 3. Peptide mapping of tryptic hydrolysates yielded 27 to 30 fluorescamine positive spots, about half the number of lysyl and arginyl residues in a polypeptide chain. 4. The findings indicate that a subunit of Ascaris hemoglobin consists of two structural units of roughly equal size, corresponding to two recurring sequences, connected together by the continuity of the polypeptide chain.