title: Quaternary structure of erythrocruorin from the nematode Ascaris suum. Evidence for unsaturated haem-binding sites.
abstract: The quaternary structure of erythrocruorin from the nematode Ascaris suum was studied. The native protein had a sedimentation coefficient, at a protein concentration of 1 mg/ml, of 11.6 +/- 0.3 S and an Mr, as determined by sedimentation equilibrium, of 332,000 +/- 17,000. SDS/polyacrylamide-gel electrophoresis gave one band with a mobility corresponding to an Mr of 43,000 +/- 2000. The Mr of the polypeptide chain was determined to be 41,600 +/- 1,500 by sedimentation equilibrium in 6 M-guanidinium chloride and 0.1 M-2-mercaptoethanol. Cross-linking with glutaraldehyde followed by SDS/polyacrylamide-gel electrophoresis yielded a maximal number of eight bands. The haem content of Ascaris erythrocruorin was observed to vary from one preparation to another. This finding was shown to be due to non-realization of the full binding capacity for haem. By titration with haemin, the haem content was found to attain a maximal value of 2.86 +/- 0.14%, corresponding to a minimal Mr per haem group of 21,000 +/- 1,000. Our findings indicate that Ascaris suum erythrocruorin is composed of eight identical polypeptide chains, carrying two haem sites each.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001200:Ascaris / Q000032:analysis*; D001665:Binding Sites; D003432:Cross-Linking Reagents; D004902:Erythrocruorins; D005976:Glutaral; D006418:Heme / Q000032:analysis*; D006427:Hemin / Q000378:metabolism; D006454:Hemoglobins; D046911:Macromolecular Substances; D013053:Spectrophotometry; D014461:Ultracentrifugation
chemical_list: D000596:Amino Acids; D003432:Cross-Linking Reagents; D004902:Erythrocruorins; D006454:Hemoglobins; D046911:Macromolecular Substances; D006418:Heme; D006427:Hemin; D005976:Glutaral