Denaturant effects on HbGp hemoglobin as monitored by 8-anilino-1-naphtalene-sulfonic acid (ANS) probe

Abstract

Glossoscolex paulistus extracellular hemoglobin (HbGp) stability has been monitored in the presence of denaturant agents. 8-Anilino-1-naphtalene-sulfonic acid (ANS) was used, and spectroscopic and hydrodynamic studies were developed. Dodecyltrimethylammonium bromide (DTAB) induces an increase in ANS fluorescence emission intensity, with maximum emission wavelength blue-shifted from 517 to 493nm. Two transitions are noticed, at 2.50 and 9.50mmol/L of DTAB, assigned to ANS interaction with pre-micellar aggregates and micelles, respectively. In oxy-HbGp, ANS binds to protein sites less exposed to solvent, as compared to DTAB micelles. In DTAB–HbGp–ANS ternary system, at pH 7.0, protein aggregation, oligomeric dissociation and unfolding were observed, while, at pH 5.0, aggregation is absent. DTAB induced unfolding process displays two transitions, one due to oligomeric dissociation and the second one, probably, to the denaturation of dissociated subunits. Moreover, guanidine hydrochloride and urea concentrations above 1.5 and 4.0mol/L, respectively, induce the full HbGp denaturation, with reduction of ANS-bound oxy-HbGp hydrophobic patches, as noticed by fluorescence quenching up to 1.0 and 5.0mol/L of denaturants. Our results show clearly the differences in probe sensitivity to the surfactant, in the presence and absence of protein, and new insights into the denaturant effects on HbGp unfolding.