On the stability of the extracellular hemoglobin of Glossoscolex paulistus, in two iron oxidation states, in the presence of urea

► Urea induces the oligomeric dissociation, denaturation and iron oxidation of HbGp. ► Oxy-, cyanomet- and met-HbGp show good fits on the basis of a three-state model. ► The intermediate states for oxy- and cyanomet-HbGp are similar to the native one. ► The two transitions observed are due to oligomeric dissociation and denaturation. ► The order of stability of the HbGp forms is given by cyanomet- > oxy- > met-HbGp.