Binding patterns of vanadium to transferrin in healthy human serum studied with HPLC/high resolution ICP-MS

Vanadium (V) is an essential metal for mammals. It has different valence states. In blood, V is bound to transferrin (Tf), a glycoprotein that has two metal-binding sites (C-lobe site and N-lobe site). In the present study, the binding patterns of V to serum Tf were analyzed by combined on-line HPLC and high-resolution ICP-MS (HPLC/HR-ICP-MS). The levels of (51)V, (56)Fe and (32)S, which are interfered with polyatomic ions such as (35)Cl(16)O(+), (38)Ar(13)C(+) and (37)Cl(14)N(+), (40)Ar(16)O(+) and (40)Ca(16)O(+), and (16)O(2)(+), respectively, when using quadrupole ICP-MS, could be monitored simultaneously by HR-ICP-MS at a resolution of m/[capital Delta]m= 4000. Sample (a 1 ml portion of serum from a healthy person or 2 mg of human serum Tf (hTf)) was directly subjected to HPLC equipped with an anion-exchange column. V in human serum without any in vitro V spike was detected as V(C)-Tf (V bound to C-lobe site of Tf) and metal(2)-Tf. Since V(iii) was most favorable in terms of the binding to hTf in the presence of bicarbonate and V bound to the C-lobe site of hTf was detected only in the case of V(iii) among the three valence states of V, it was suggested that a part, at least, of V in the V(C)-Tf in healthy human serum may be present as V(iii), in addition to the generally accepted V(iv).