Fe-nitrilotriacetic acid--binding proteins associated with rat liver plasma membranes

The uptake of nontransferrin-bound iron by hepatocytes is known to occur and may contribute to the deposition of iron and resulting injury during hemochromatosis. To examine the proteins that may function in the transport of nontransferrin-bound iron, the properties of FeNTA-binding to rat liver basolateral plasma membranes were characterized. The binding of 55FeNTA to purified liver basolateral plasma membranes was measured using a simple centrifugation assay. The binding activity could be solubilized with 0.1% octylglucoside; apparent molecular weight Mapp approximately 210 kd for the binding complex was determined by gel filtration chromatography. Immobilized metal affinity chromatography was used to further purify binding protein(s) from rat liver plasma membranes and at least six polypeptides were identified by silver staining. If associated in a stoichiometric complex, the molecular mass of these proteins would predict a size of approximately 227 kd in fairly close agreement with the gel filtration experiments. The characterization of FeNTA-binding proteins associated with basolateral membranes is the first step towards understanding elements responsible for the uptake of nontransferrin-bound iron by the liver.