title: Erythrocruorin from the crustacean Caenestheria inopinata. Quaternary structure and arrangement of subunits.
abstract: The subunit structure of erythrocruorin from the crustacean Caenestheria inopinata was studied. The native protein was found to have a sedimentation coefficient of 12.0 S and a molecular weight, as determined by sedimentation equilibrium, of 302,000. Iron and heme determinations gave 0.346 and 3.98% corresponding to minimal molecular weights of 16,100 and 15,500, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis gave one band with mobility corresponding to a molecular weight of 30,000. The molecular weight of the polypeptide chain was determined to be 30,500 by sedimentation equilibrium in 6 M guanidine hydrochloride and 0.1 M 2-mercaptoethanol. Dissociation of the 12S molecule was observed at acidic and alkaline pH. A dissociation species of 2.7 S was isolated and its molecular weight determined to be 28,000 by sedimentation equilibrium. On a molecular weight basis, the native molecule is composed of ten 2.7S subunits, each of which consists of a single polypeptide chain carrying two hemes. We propose a model for the molecule composed of ten spheres, each representing a 2.7S subunit, arranged in two layers stacked in an eclipsed orientation, in five spheres of each layer occupying the vertices of a regular pentagon. Support for this arrangement is provided by a comparison of projections of the model with molecular profiles seen in the electron microscope.
mesh_terms: D000818:Animals; D003445:Crustacea; D004591:Electrophoresis, Polyacrylamide Gel; D004902:Erythrocruorins; D006418:Heme / Q000032:analysis; D006454:Hemoglobins; D007501:Iron / Q000032:analysis; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008958:Models, Molecular; D008970:Molecular Weight; D011487:Protein Conformation
chemical_list: D004902:Erythrocruorins; D006454:Hemoglobins; D046911:Macromolecular Substances; D006418:Heme; D007501:Iron