Loss or deficiency in which of the following proteins would result in the inability of transferrin bind and transport iron in the blood?

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Hephaestin is a ferroxidase enzyme that facilitates the conversion of Fe2+ to Fe3+, which is necessary for iron to bind to transferrin for transport in the blood. Without hephaestin, this conversion cannot occur, impairing transferrin's ability to bind and transport iron.  Transferrin can only bind the ferric form of iron within the circulation. Within the cells iron is stored, bound to ferritin in the ferrous form. Iron is transported across the basolateral membrane of intestinal enterocytes into the circulation, through the action of the transport protein ferroportin (also called IREG1 = iron-regulated gene 1). Associated with ferroportin is the enzyme hephaestin (a copper-containing ferroxidase with homology to ceruloplasmin) which oxidizes the ferrous form back to the ferric form. Once in the circulation, ferric form of iron is bound to transferrin and passes through the portal circulation of the liver.

Loss or Deficiency in Which of the Following Proteins Would