Inhibitory effect of Zn(II) on diferric-transferrin complex formation.

(A) Initial rates of diferric-transferrin formation at 460 nm are plotted versus concentration of Zn(II). Concentration of apo-transferrin was 80 µM and that of Fe(II) was 200 µM. (B) Comparison of the inhibitory effect of Zn(II) on the diferric-transferrin complex formation for the non-enzymatic oxidation of Fe(II) by molecular oxygen in the presence of transferrin (Tf 70 µM) and for the ferroxidase activity of ceruloplasmin (CP 0.08 µM) measured with the transferrin assay. Final concentration of Fe(II) was 60 µM and that of Zn(II) was 70 µM. Measurements were done in 100 mM Hepes buffer, 100 mM NaCl, pH 7.2 in triplicate at 37°C.