LIGAND-FREE FORM OF HUMAN ALPHA-FETOPROTEIN - EVIDENCE FOR THE MOLTENGLOBULE STATE

By means of circular dichroism and fluorescence spectroscopy, viscomet ry and scanning microcalorimetry we have shown that the release of lig ands from human alpha-fetoprotein (AFP) results in a considerable rear rangement of the protein molecule, Ligand-free form is practically as compact as the native molecule and has native-like content of secondar y structure but no rigid tertiary structure. This means that the relea se of ligands transforms the AFP molecule into a molten globule state. Stripping the ligands from AFP is the irreversible process, i.e., nat ive protein molecule cannot be reconstituted from the ligand-free form of AFP by adding back ligands. A possible functional role of such a s tructural transformation is discussed. (C) 1997 Federation of European Biochemical Societies.