© 1980 by The Society for Integrative and Comparative Biology
Structure of Annelid High Molecular Weight Hemoglobins (Erythrocruorins)1
Department of Zoology. The University of Texas at Austin Austin Texas 78712
The extracellular vascular hemoglobins (erythrocruorins) of annelids are polymeric oxygen carriers with molecular weights of approximately 3 x 106 or about 46 times the molecular weight of a vertebrate hemoglobin tetramer. The molecule appears as a dodecamer of 12 large submultiples arranged at the vertices of two regular hexagons one on top of the other in electron micrographs. The dimensions are about 250 Å across the face of the hexagon and about 170 Å in height. The molecular weight of a one-twelfth submultiple is approximately 250 000. Biochemical studies suggest that each submultiple contains 16 to 18 subunits and that the intact hemoglobin molecule contains approximately 200 subunits. Unlike vertebrate hemoglobin which contains one heme moiety for each polypeptide chain the annelid hemoglobins apparently contain one heme per 15 to 20 chains. The reasons for this lack of a 11 heme chain stoichiometry are not known at present. One possibility may be that it is the result of insufficient purification of the hemoglobin. Alternatively, more than one globin chain might share a heme certain globin chains might lack the heme moiety and have a non hemoglobin function, or certain globin chains may lose their heme during purification of the hemoglobin. We are presently determining the amino acid sequence of one globin chain of Lumbricus terrestris hemoglobin. This information should be helpful in understanding the structure of these interesting polymers.