CHARACTERIZATION AND PARTIAL-PURIFICATION OF A FERRIREDUCTASE FROM HUMAN DUODENAL MICROVILLUS MEMBRANES

Reduction of ferric iron in the presence of HuTu 80 cells or duodenal microvillus membranes (MVMs) was investigated. With both systems, NADH -dependent reduction of Fe3+/NTA (nitrilotriacetic acid) was demonstra ted, using the ferrous iron chelator ferrozine. Uptake of Fe3+ from Fe 3+/NTA by HuTu 80 cells was strongly inhibited by addition of ferrozin e, indicating that Fe2+ is the substrate for the iron uptake system. W ith isolated plasma membranes it is shown that the reductase activity is sensitive to trypsin and incubation at 65 degrees C. The reductase activity could be extracted from the plasma membrane and partially pur ified by ammonium sulphate precipitation and isoelectric focusing. Fro m the purification and inhibition characteristics we conclude that red uction of ferric iron on the surface of duodenal plasma membranes is c atalysed by a membrane protein.