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

The interaction of (VO)-O-IV-salts as well as of a few (VO)-O-IV(carrier)(n) complexes with human serum transferrin (hTF) is studied focusing on the determination of the nature and stoichiometry of the binding of (VO2+)-O-IV to hTF, as well as whether the conformation of hTF upon binding to (VO2+)-O-IV or to its complexes is changed. Circular dichroism (CD) spectra measured for solutions containing (VO2+)-O-IV and apo-hTF, and (VO)-O-IV-maltol and apo-hTF, clearly indicate that hTF-(VO)-O-IV-maltol ternary species form with a (VO)-O-IV:maltol stoichiometry of 1:1. For (VO)-O-IV salts and several (VO)-O-IV(carrier)(n) complexes (carrier ligand = maltolato, dhp, picolinato and dipicolinato) (Hdhp = 1,2-dimethyl-3-hydroxy-4-pyridinone) the maximum number of (VO2+)-O-IV bound per mole of hTF is determined to be similar to 2 or lower in all cases. The binding of (VO)-O-IV 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 ((VO)-O-IV)(2)hTF species may occur with the closing of the hTF conformation as is the case in (Fe-III)(2)hTF, which is an essential feature for the transferrin receptor recognition. (c) 2013 Elsevier Inc. All rights reserved.