On the stability of the 24-meric hemocyanin from Eurypelma californicum

The stability of the 24-meric hemocyanin from Eurypelma californicum towards various denaturants (GdnHCl, urea, urea derivatives and salts of the Hofmeister series) indicates that the quaternary structure is stabilized by hydrophilic and polar forces. Thus, the interaction between the seven different subunit types of this cheliceratan hemocyanin is comparable with that of the closely related crustacean hemocyanins. In contrast, no significant influence of divalent ions such as Ca2+ and Mg2+ on the stability is observed at pH 8.0 and pH 8.5 but not at pH 7.0. Studies, both in the presence of urea and GdnHCl indicate that the denaturation process consists of a dissociation of the oligomeric structure into intact subunits at lower concentrations of denaturants followed by denaturation of the subunits at higher concentrations of denaturants. No intermediates such as hexamers or dodecamers were detected after 24 h of incubation. This study also reveals that oligomerization has a stabilizing effect on the heterogeneous subunits. In addition, differences in the primary structures result in different stabilities of the seven different subunit types.