Binding patterns of co-existing aluminium and iron to human serum transferrin studied by HPLC–high resolution ICP-MS

Abstract

Serum transferrin (Tf) is an iron-binding glycoprotein. Aluminium in the blood is bound to the transferrin. In the present study, the chemical forms of co-existing Al and Fe bound to human serum Tf were studied by combined on-line HPLC and high-resolution ICP-MS (HPLC-HR-ICP-MS). Samples were subjected to HPLC equipped with an anion-exchange column. The levels of ²⁷Al, ⁵⁶Fe and ³²S, which are interfered with by polyatomic ions such as ¹³C¹⁴N⁺, ¹²C¹⁵N⁺ and ¹²C¹⁴N¹H⁺, ⁴⁰Ar¹⁶O⁺ and ⁴⁰Ca¹⁶O⁺, and ¹⁶O₂⁺, respectively, when using quadrupole ICP-MS, were monitored simultaneously by HR-ICP-MS at a resolution of m/Δm = 3000. Al added to apo-Tf as Al-citrate was preferentially bound to the N-lobe site almost selectively. Al in serum from a healthy person without any in vitro Al spike was present both as Al_N-Tf and Al_N,Fe_C-Tf. The chemical states were reproduced in the apo-Tf solution supplemented with Fe (Fe/Tf ratio = 0.6) and Al (Al/Tf ratio = 1) successively. The ³²S level was useful for monitoring the protein levels in the HPLC eluate. The clean-up column procedures employed reduced the detection limit for ²⁷Al to 0.1 μg l^–1 (3s_B) at the middle resolution.