FE-NITRILOTRIACETIC ACID-BINDING PROTEINS ASSOCIATED WITH RAT-LIVER PLASMA-MEMBRANES

The uptake of nontransferrin-bound iron by hepatocytes is known to occ ur and may contribute to the deposition of iron and resulting injury d uring hemochromatosis. To examine the proteins that may function in th e transport of nontransferrin-bound iron, the properties of FeNTA-bind ing to rat liver basolateral plasma membranes were characterized. The binding of (55)FeNTA to purified liver basolateral plasma membranes wa s measured using a simple centrifugation assay. The binding activity c ould be solubilized with 0.1% octylglucoside; apparent molecular weigh t M(app) similar to 210 kd for the binding complex was determined by g el filtration chromatography. Immobilized metal affinity chromatograph y was used to further purify binding protein(s) from rat liver plasma membranes and at least six polypeptides were identified by silver stai ning. If associated in a stoichiometric complex, the molecular mass of these proteins would predict a size of similar to 227 kd in fairly cl ose agreement with the gel filtration experiments. The characterizatio n of FeNTA-binding proteins associated with basolateral membranes is t he first step towards understanding elements responsible for the uptak e of nontransferrin-bound iron by the liver.