Subunit structure of hemoglobins from erythrocytes of the blood clam, Anadara broughtonii.

Intracellular hemoglobins of the sea blood clam Anadara broughtonii consist of HbI dimer (33%) and HbII tetramer (60%). The molecular weights of globins of HbI and HbII were determined by sodium dodecyl sulfate (SDS)-gel electrophoresis to be 15,500 and 16,500, respectively. The existence of two dissimilar chains, alpha and beta, in globin from HbII tetramer was confirmed electrophoretically and the chains were separated by CM-cellulose chromatography in 8 M urea. In contrast, globin from HbI dimer showed a single band on two types of electrophoresis. The NH2-terminus and the COOH-terminus of HbI were determined to be proline and leucine, respectively. From the results of finger-printing, the alpha and beta chains from HbII were considered to have a rather similar profile, whereas globin from HbI was very different. The results obtained by amino acid analysis of each chain also supported the above findings. It was thus shown that HbII has an alpha2beta2 subunit structure, which is rare among invertebrate hemoglobins. On the other hand, HbI seems to have two identical subunits, designated as "gamma", and to exist as a "gamma2" dimer structure. Both Anadara Hb's appear to have no functional groups relating to the Bohr effect and to be unable to form a binding site for organic phosphates.