title: Studies on Scapharca hemoglobins. Properties of the dimeric protein reconstituted with Fe- or Co-porphyrin.
abstract: A native globin from the dimeric hemoglobin, hemoglobin I, of the mollusc Scapharca inaequivalvis has been obtained with the acid-acetone method. The globin has a lower sedimentation coefficient than the native protein at neutral pH; its reconstitution product with natural heme has the same physicochemical and functional properties as the native protein. proto- and meso-cobalt hemoglobin I have been prepared and characterized. proto-Cobalt hemoglobin I binds oxygen reversibly with a lower affinity and a lower cooperativity than native hemoglobin I; thus, the changes in the functional properties brought about by substitution of iron with cobalt are similar to those observed in human hemoglobin A. The EPR spectra of deoxy-proto-cobalt hemoglobin I and of the photolysis product of oxy-meso-cobalt hemoglobin I indicate that two histidine residues are the apical heme ligands. The broad signal at g = 2.38 in deoxy-proto-cobalt hemoglobin I points to a constrained structure of the heme site in this derivative which results from a distorted coordination of the hindered proximal histidine. A similar structure has been proposed previously for the alpha chains in deoxy-cobalt hemoglobin A.
mesh_terms: D001059:Apoproteins; D049872:Bivalvia; D003035:Cobalt; D004578:Electron Spin Resonance Spectroscopy; D005914:Globins; D006418:Heme; D006427:Hemin; D006454:Hemoglobins; D007501:Iron; D046911:Macromolecular Substances; D010100:Oxygen; D013057:Spectrum Analysis
chemical_list: D001059:Apoproteins; D006454:Hemoglobins; D046911:Macromolecular Substances; D003035:Cobalt; D006418:Heme; D006427:Hemin; D005914:Globins; D007501:Iron; D010100:Oxygen