Thermal stability of extracellular hemoglobin of Rhinodrilus alatus (HbRa): DLS and SAXS studies

Made available in DSpace on 2018-11-26T17:06:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-09-01 Oxy-HbRa thermal stability was evaluated by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) at pH 5.0, 7.0, 8.0, and 9.0. DLS results show that oxy-HbRa, at pH 7.0 and 5.0, remains stable up to 56 degrees C, undergoing denaturation/aggregation in acidic media above 60 degrees C, followed by partial sedimentation of aggregates. At alkaline pH values 8.0 and 9.0, oxy-HbRa oligomeric dissociation is observed above 30 degrees C, before denaturation. SAXS data show that oxy-HbRa, at 20 degrees C, is in its native form, displaying radius of gyration (R-g) and particle maximum dimension (D-max) of 108 +/- 1 and 300 +/- 10 angstrom, respectively. Oxy-HbRa, at pH 7.0, undergoes denaturation/aggregation at 60 degrees C. At pH 5.0-6.0, HbRa thermal denaturation/aggregation start earlier, at 50 degrees C, accompanied by an increase of R-g and D-max values. However, an overlap of oligomeric dissociation and denaturation in the system is observed upon temperature increase, with an increase in R-g and D-max. Analysis of experimental p(r) curves as a linear combination of theoretical curves obtained for HbGp fragments from the crystal structure shows an increasing contribution of dodecamer (abcd)(3) and tetramer (abcd) in solution, as a function of pH values (8.0 and 9.0) and temperature. Finally, our data show, for the first time, that oxy-HbRa, in neutral and acidic media, does not undergo oligomeric dissociation before denaturation, while in alkaline media the oligomeric dissociation process is an important step in the thermal denaturation. Inst Quim Sao Carlos, Sao Carlos, SP, Brazil Univ Estado Mato Grosso, Barra Do Bugres, MT, Brazil Univ Estadual Paulista, Registro, SP, Brazil Univ Estadual Paulista, Registro, SP, Brazil