A protein that helps the body pump iron.

To the human body, iron is a metal more precious than gold. Among its vital roles, iron helps form oxygen-carrying hemoglobin molecules in the blood. More than a billion people worldwide suffer from anemia because they have too little iron in their diet. Even in the United States, I woman in 10 is anemic.

Despite the metal's importance, scientists have had few clues as to how the body snares iron from food and transfers it into cells.

"The molecular details of iron absorption have eluded investigators for half a century. There have been many reports about one molecule or another serving as an iron transporter, none of which have withstood scrutiny and time," says Philip Aisen of the Albert Einstein College of Medicine in New York.

Now, two research groups have independently homed in on a protein that seems to be the long-sought treasure.

"It looks like this protein is the major iron transporter, both in the intestine and other tissues," says Nancy C. Andrews of the Howard Hughes Medical Institute at Children's Hospital in Boston.

Andrews and her colleagues, who present their work in the August Nature Genetics, studied mice with a hereditary form of anemia and found that the disorder stemmed from a mutation in a previously known gene called Nramp2.

A second line of evidence implicating the gene, presented by a research team led by Matthias A. Hediger of Brigham and Women's Hospital in Boston, appears in the July 31 Nature.

These investigators fed rats an iron-poor diet, hoping the animals would compensate by increasing their production of iron transporter proteins. The researchers then isolated the protein-encoding RNA strands from the intestinal cells of the animals and created from the RNA a library of genes. They injected individual genes into frog eggs, placed the eggs into an iron-rich solution, and observed which ones took in large amounts of the metal...

They discovered a single rat gene that endowed the frog eggs with an ability to absorb extra iron. That gene was Nramp2. Hediger's team also found that Nramp2 helps the eggs absorb other metals, such as copper, zinc, and cadmium.

The Nramp2 gene resembles another gene, Nramp1, whose protein plays a crucial role in animals' resistance to bacteria that invade their cells. Like people, bacteria need iron to survive, notes Andrews. Nramp1's protein "may keep iron away from intracellular pathogens," she speculates.

On the other hand, suggests Hediger, this protein may pump iron into infected cells to help produce antibacterial compounds.

While Aisen believes that the two groups have found the long-sought iron transporter, he notes that they haven't determined how it latches onto iron and delivers the metal into cells.

The researchers speculate that drugs or other therapies targeting the iron transporter may help treat anemia or its common counterpart, hemochromatosis, a disease in which the body absorbs too much iron (SN: 1/18/97, p. 46).