title: On the temperature stability of extracellular hemoglobin of Glossoscolex paulistus, at different oxidation states: SAXS and DLS studies.
abstract: Glossoscolex paulistus hemoglobin (HbGp) was studied by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). DLS melting curves were measured for met-HbGp at different concentrations. SAXS temperature studies were performed for oxy-, cyanomet- and met-HbGp forms, at several pH values. At pH 5.0 and 6.0, the scattering curves are identical from 20 to 60 °C, and Rg is 108 Å, independent of the oxidation form. At pH 7.0, protein denaturation and aggregation occurs above 55 °C and 60 °C, for oxy and met-HbGp, respectively. Cyanomet-HbGp, at pH 7.0, is stable up to 60 °C. At alkaline pH (8.0-9.0) and higher temperature, an irreversible dissociation process is observed, with a decrease of Rg, Dmax and I(0). Analysis by p(r), obtained from GNOM, and OLIGOMER, was used to fit the SAXS experimental scattering curves by a combination of theoretical curves obtained for HbLt fragments from the crystal structure. Our results show clearly the increasing contribution of smaller molecular weight fragments, as a function of increasing pH and temperature, as well as, the order of thermal stabilities: cyanomet->oxy->met-HbGp.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo/São Carlos, SP, Brazil.
authors.forename: José Wilson P
authors.initials: JW
authors.lastname: Carvalho
authors.forename: Patrícia S
authors.initials: PS
authors.lastname: Santiago
authors.forename: Tatiana
authors.initials: T
authors.lastname: Batista
authors.forename: Carlos Ernesto Garrido
authors.initials: CE
authors.lastname: Salmon
authors.forename: Leandro R S
authors.initials: LR
authors.lastname: Barbosa
authors.forename: Rosangela
authors.initials: R
authors.lastname: Itri
authors.forename: Marcel
authors.initials: M
authors.lastname: Tabak
mesh_terms: D000818:Animals; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D008027:Light; D008706:Methemoglobin / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D009835:Oligochaeta / Q000378:metabolism*; D010084:Oxidation-Reduction; D055550:Protein Stability; D012542:Scattering, Radiation; D053838:Scattering, Small Angle; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D006454:Hemoglobins; C007169:cyanomethemoglobin; D008706:Methemoglobin; D007501:Iron