The long range goal of this research is a better understanding of the basic mechanism and regulation of iron metabolism, which would, in turn, lead to a better understanding of metabolic disorders, such as iron deficiency anemia or abnormal increase of body iron known as hemochromatosis. In particular, this research project would attempt to assess the importance of a recently discovered inhibitory protein of the serum ferroxidases in the regulation of the efflux of iron from storage tissues. The serum of animals maintained on diets of varying iron content will be examined to see if different levels of the ferroxidase inhibitor exist. Variations in the serum level of the inhibitor could control the amount of ferroxidase activity exhibited by the serum ferroxidases and thus alter the rate of iron mobilization from tissue stored in response to changes in the amounts of iron entering the relatively constant plasma iron pool from other sources. The ferroxidase inhibitory protein from rabbit serum, has been purified and partially characterized. The presence of a similar inhibitory substance has been detected in human serum. The ferroxidase inhibitor of human serum will be purified and characterized and its structure compared to the rabbit serum inhibitor. Kinetic studies with the rabbit and human inhibitor will be undertaken in an attempt to decipher the molecular mode of action of the inhibitor in the ferroxidase reaction.