Interaction of vanadium(IV) with human serum apo-transferrin

Abstract

The interaction of VIVO-salts as well as of a few VIVO(carrier)n complexes with human serum transferrin (hTF) is studied focusing on the determination of the nature and stoichiometry of the binding of VIVO2+ to hTF, as well as whether the conformation of hTF upon binding to VIVO2+ or to its complexes is changed. Circular dichroism (CD) spectra measured for solutions containing VIVO2+ and apo-hTF, and VIVO–maltol and apo-hTF, clearly indicate that hTF–VIVO–maltol ternary species form with a VIVO:maltol stoichiometry of 1:1. For VIVO salts and several VIVO(carrier)n complexes (carrier ligand=maltolato, dhp, picolinato and dipicolinato) (Hdhp=1,2-dimethyl-3-hydroxy-4-pyridinone) the maximum number of VIVO2+ bound per mole of hTF is determined to be ~2 or lower in all cases. The binding of VIVO to apo-hTF most certainly involves several amino acid residues of the Fe-binding site, and as concluded by urea gel electrophoresis experiments, the formation of (VIVO)2hTF species may occur with the closing of the hTF conformation as is the case in (FeIII)2hTF, which is an essential feature for the transferrin receptor recognition.