Human transferrin is a blood plasma protein for iron ion delivery encoded by the TF gene. The gene coding for transferrin in humans is located in chromosome band 3q21. Transferrin is a glycoprotein, which binds iron very tightly but reversibly. Transferrin contains 2 specific high-affinity Fe (III) binding sites. The affinity of transferrin for Fe (III) is extremely high (1023 M-1 at pH 7.4) but decreases progressively with decreasing pH below neutrality. The metal binding properties of transferrin have a great influence on the biochemistry of plutonium.