Perspectives in Iron Metabolism

IN early times the earth had a reducing atmosphere, and an abundance of ferrous iron was present for incorporation into biologic molecules.1 Later, with an increase in atmospheric oxygen, iron existed largely in its less available ferric form,2 and special devices had to be developed by life forms for the acquisition of iron. Bacteria, for example, synthesize and excrete high-affinity chelating agents that extract otherwise unavailable iron from the surrounding environment.3 The roots of plants also secrete substances that augment iron absorption.4 In mammalian species a "shuttle" protein in the upper intestine — mucosal transferrin — appears to perform this . . .