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

pH effects on the oligomeric structure of giant Glossoscolex paulistus extracellular hemoglobin in the oxy- and met-forms have been studied as well as effects of the addition of anionic sodium dodecyl sulfate surfactant. A radius of gyration of 110 Angstrom 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 (I(0)) decreases a factor of 2.5, indicating protein dissociation. At 20 mM surfactant, further I( 0) decrease is observed, with a reduction of radius of gyration to approximately 30 Angstrom 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 Angstrom shows that the giant hemoglobin dissociation into small subunits also occurs at alkaline pH. From the I( 0) 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 Angstrom 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.