It has been previously suggested that large amounts of
oxalate in plasma could play a role in
autism by binding to the bilobal
iron transport protein transferrin (hTF), thereby interfering with
iron metabolism by inhibiting the delivery of
iron to cells. By examining the effect of the substitution of
oxalate for the physiologically utilized synergistic
carbonate anion in each lobe of hTF, we sought to provide a molecular basis for or against such a role. Our work clearly shows both qualitatively (6 M
urea gels) and quantitatively (kinetic analysis by stopped-flow spectrofluorimetry) that the presence of
oxalate in place of
carbonate in each binding site of hTF does indeed greatly interfere with the removal of
iron from each lobe (in the absence and presence of the specific hTF receptor). However, we also clearly demonstrate that once the
iron is bound within each lobe of hTF, neither
anion can displace the other. Additionally, as verified by
urea gels and electrospray mass spectrometry, formation of completely homogeneous hTF-
anion complexes requires that all
iron must first be removed and hTF then reloaded with
iron in the presence of either
carbonate or
oxalate. Significantly, experiments described here show that
carbonate is the preferred binding partner; i.e., even if an equal amount of each
anion is available during the
iron loading process, the hTF-
carbonate complex is formed.