Physiological iron chelators pyrophosphate and citrate have different effects on the proportions of monoferric transferrin metalloforms.

Human serum transferrin can bind up to two iron atoms, one in each of its two domains which are known as the N-lobe and the C-lobe. Ferric pyrophosphate and ferric citrate have been shown to direct loading into the C-lobe and N-lobe, respectively. We report that the iron supplement ferric pyrophosphate citrate directs iron to the C-lobe.