Comparison of interaction between ceruloplasmin and lactoferrin/transferrin: to bind or not to bind

The year 2016 marked the 50th anniversary of the discovery by S. Osaki who first showed that ceruloplasmin (CP, ferro:O-2-oxidoreductase or ferroxidase) is capable of oxidizing Fe(II) to Fe(III) and favors the incorporation of the latter into transferrin (TF). However, much debate remains in the literature concerning the existence of a complex between the enzyme oxidizing iron and the protein facilitating its transport in plasma. We studied CP in exocrine fluids and demonstrated its high-affinity interaction with transferrin found in breast milk and in lacrimal fluid, i.e. with lactoferrin (LF). Here we present data obtained by comparing the interaction of CP with LF and TF using surface plasmon resonance and Hummel-Dreyer chromatography. Binding of apo-LF within the range of concentrations 1.6-51.3 mu M with CP immobilized on a CM5-chip is characterized by K (D) = 1.07 mu M. Under similar conditions, the K (D) for apo-TF was measured and appeared to be higher than 51.3 mu M. Hummel-Dreyer chromatography of CP with 51 mu M apo-LF/apo-TF in the effluent demonstrated the absence of interaction between apo-TF and CP in solution, contrary to efficient interaction between apoLF and CP. In contrast to LF, the interaction of apo-TF with CP is probably not stable within the physiological range of concentrations of TF.