COPPER(II)-BINDING ABILITY OF HUMAN ALPHA-FETOPROTEIN

Abstract

The Cu(II)-binding ability of human .alpha.-fetoproteins purified from umbilical cord serum and from ascites fluid of a hepatoma-bearing patient was examined by equilibrium dialysis and gel filtration. The pH dependence of the Cu(II)-binding ability of .alpha.-fetoprotein was quite similar to that of albumin. .alpha.-Fetoprotein bound 1 mol of Cu(II) ion/mol of protein above pH 6.0 and 0.5 mol of Cu(II) ion at pH 5.4, which is close to the pK value of the imidazole group of histidine. Photooxidation of .alpha.-fetoprotein in the presence of methylene blue resulted in the loss of the Cu(II)-binding ability of the protein in parallel with the destruction of the histidyl residues. A synthetic amino-terminal undecapeptide of .alpha.-fetoprotein also bound Cu(II) ion. The histidyl residue at the amino-terminal region of .alpha.-fetoprotein apparently plays an important role in the Cu(II)-binding ability of the protein.