The effects of Ce3+ and Ce4+ on the stability of fibroblast growth factor-2

The interaction between tri or tetravalent cerium ions and basic fibroblast growth factor (FGF-2) at 0.1-6: 1 molar ratio under physiological condition was studied by fluorescence and CD spectrum. The different spectra alterations of FGF-2 induced by Ce 3+ and Ce 4+ showed that Ce 3+ and Ce 4+ caused different conformational changes of FGF-2 respectively, though both of them destabilized the protein. The instability of FGF-2 in the presence of Ce 3+ is involved in the oxidation of its free cystein of protein, but that this treatment nearly does not affect the biological activity. As to Ce 4+ , it not only induced the conformational changes of protein but also inhibits its activity in a dose-dependent manner, which could be relative to the electrostatic repulsion between Ce 4+ and its basic amino acid residues (pI=9.6) or the specific binding of Ce 4+ to deprotonated amino acid residues. The interesting results would be helpful to investigate the problem of the stability of proteins.