The hemoglobins of Phoronopsis viridis, of the primitive invertebrate phylum phoronida: Characterization and subunit structure☆

Abstract The primitive invertebrate, Phoronopsis viridis , of the phylum Phoronida, has intra-cellular hemoglobins composed of four unique polypeptide chains, two of which associate to form hetero- and homodimers and two which do not associate at all. The CO-derivatives of the associating chains are completely dimeric; removal of the ligand does not result in further aggregation as it does in several other invertebrate hemoglobins. Oxidation of the associating hemoglobins is accompanied by dissociation to monomers, but the cyanide derivative of the methemoglobin is dimeric. The four polypeptide chains all have molecular weights of about 16,000 as determined by iron content and gel electrophoresis with sodium dodecyl sulfate. The two associating chains form three components with isoelectric points at pH 5.6, 5.9, and 6.9 whereas those for the two monomeric chains are at pH 6.2 and 7.9. The chains have been characterized by amino acid composition, tryptic peptide patterns, and the amino acid sequence of the NH 2 -terminal segment. The oxygen equilibrium of a dimeric fraction has been determined at pH 7.5 and 20 °C; the pressure of half-saturation is 2.3 mm Hg.