Speciation of Aluminium in Human Serum Investigated by HPLC/High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS) : Effects of Sialic Acid Residues of the Carbohydrate Chain on the Binding Affinity of Aluminium for Transferrin

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Aluminium (Al) in the blood is bound to transferrin (Tf), a glycoprotein of about 80kDa that is characterized by its need for a synergistic anion. The binding affinity of both Al and iron (Fe) for Tf is surveyed in the context of our recent studies by on-line high-performance liquid chromatography/high-resolution inductively coupled plasma mass spectrometry (HPLC/HR-ICP-MS). First, Al in human serum without any in vitro Al-spikes was present in a form bound to the N-lobe site of human serum Tf (hTf). Next, the effects of sialic acid in the carbohydrate chain of hTf on the binding affinity of Al (or Fe) for hTf were studied by using asialo-hTf obtained by treating hTf with sialidase. The binding affinity of Fe for asialo-hTf and native-hTf was similar, but the binding affinity of Al for asialo-hTf was greater than that for native-hTf. These findings are discussed in relation to diseases in which the serum concentrations of carbohydrate-deficient Tf and oxalate are increased.
2009-04-01