Iron is released from macrophages, hepatocytes, and enterocytes into circulation by which membrane protein?

The correct answer to this question is ferroportin. This protein plays a critical role in the export of iron from cells into the bloodstream. Ferroportin is found in the membranes of macrophages, hepatocytes (liver cells), and enterocytes (intestinal cells), where it facilitates the release of iron that has been stored or absorbed by these cells. Once iron is transported out of these cells through ferroportin, it can bind to transferrin in the plasma, which transports it to various tissues throughout the body.

Transferrin, while important for iron transport in the circulation, does not mediate the release of iron from cells; instead, it functions after iron is already in the bloodstream. DMT1 (Divalent Metal Transporter 1) is responsible for the uptake of iron into cells rather than for its release. Ferrochelatase, on the other hand, is involved in the final step of heme synthesis, catalyzing the incorporation of iron into porphyrins, and is not related to the export of iron to circulation. Understanding the specific functions of these proteins clarifies their role in iron metabolism, supporting why ferroportin is the correct choice for the release mechanism of iron into circulation.