EVIDENCE FOR THE MOLTEN GLOBULE STATE OF HUMAN APO-CERULOPLASMIN

The conformational features of copper-free ceruloplasmin (CP), as comp ared to the hole-protein, were evaluated utilizing far- and near-UV ci rcular dichroism and fluorescence spectroscopy. The results obtained i ndicate that apo-CP maintains the secondary structure of the hole-prot ein, while the tertiary interactions are much weaker. In addition, the removal of copper from the hole-protein leads to the exposure of hydr ophobic patches to solvent, as shown by the fact that apo-CP, at varia nce from the hole-protein, binds the hydrophobic probe ANS. It is prop osed that the CP molecule, upon copper removal, acquires the conformat ional features typical of a molten globule, which might be the conform ational state of CP during its biosynthesis before metal incorporation .