title: Small angle x-ray scattering (SAXS) study of the extracellular Hemoglobin of Glossoscolex paulistus: effect of pH, iron oxidation state, and interaction with anionic SDS surfactant.
abstract: pH effects on the oligomeric structure of giant Glossoscolex paulistus extracellular hemoglobin in the oxyand met-forms have been studied as well as effects of the addition of anionic sodium dodecyl sulfate surfactant. A radius of gyration of 110 A is observed for a macromolecule. At 2 mm surfactant, the radius of gyration diminishes slightly for the oxy-form. However, the extrapolated initial scattering intensity (I0) decreases a factor of 2.5, indicating protein dissociation. At 20 mm surfactant, further I0 decrease is observed, with a reduction of radius of gyration to approximately 30 A consistent with dissociation into smaller subunits. At pH 9.0, the scattering curves are similar to that obtained for the protein in the presence of 20 mm surfactant at pH 7.0. A radius of gyration of approximately 35 A shows that the giant hemoglobin dissociation into small subunits also occurs at alkaline pH. From the I0 value, one can suggest that the tetramer is the main scatter at pH 9.0. At pH 7.0, the met-form dissociates to a larger extent at 2 mm surfactant as compared with the oxy-form, and the main scatters seem to be the 1/12 subunit. At pH 9.0, for the oxy-form, the addition of surfactant does not modify the scattering curve and a radius of gyration approximately 30 A is obtained, while for the met-form some kind of aggregation is observed. Our results give support to conclude that the iron oxidation state is an important factor modulating the oligomeric dissociation.
authors.affiliation: Departamento de Química e Física Molecular, Instituto de Química de São Carlos, Universidade de São Paulo, USP, C.P. 780, 13560-970 São Carlos, São Paulo, Brazil.
authors.forename: Emerson Luiz
authors.initials: EL
authors.lastname: Gelamo
authors.forename: Rosangela
authors.initials: R
authors.lastname: Itri
authors.forename: Marcel
authors.initials: M
authors.lastname: Tabak
mesh_terms: D000818:Animals; D000838:Anions; D000845:Annelida / Q000737:chemistry*; D005453:Fluorescence; D005583:Fourier Analysis; D006454:Hemoglobins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008706:Methemoglobin / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010108:Oxyhemoglobins / Q000737:chemistry; D012542:Scattering, Radiation; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology*; D014965:X-Rays
chemical_list: D000838:Anions; D006454:Hemoglobins; D010108:Oxyhemoglobins; D012967:Sodium Dodecyl Sulfate; D008706:Methemoglobin; D007501:Iron