Uptake of iron from transferrin by isolated rat hepatocytes. A redox-mediated plasma membrane process? (original) (raw)

1988, Journal of Biological Chemistry

both we (8) and others (13, 14) have shown that transferrin and at least part of the iron localizes to the endosomal compartment of hepatocytes. Consequently, if mechanisms other than receptor-mediated endocytosis are operating, they may be operating in parallel with or as part of receptor-mediated endocytosis. The aim of the present work was to study the importance of plasma membrane redox processes for the uptake of iron from transferrin by isolated hepatocytes. Our results suggest that at transferrin concentrations above that needed to saturate the transferrin receptors (0.1-0.5 PM (2, 3, 7)), isolated hepatocytes take up iron predominantly by mechanisms located to the plasma membrane. The process involves cooperative proton and electron fluxes with labilization of ferric iron from transferrin with subsequent reduction and translocation of iron through the plasma membrane. Thus, it would appear that only a minor part of iron accumulated by the cell is taken up by receptor-mediated endocytosis of transferrin. MATERIALS AND METHODS Chemicals-Collagenase (type IV), bovine serum albumin (essentially fatty acid-free), human transferrin (9855, essentially iron-free), CCCP,' chloroquine, methylamine, iodoacetate, monensin, and fluoresceine isothiocyanate (FITC) coupled to celite were from Sigma. Bolton and Hunter reagent for protein iodination (74 MBq/mmol) and 'VeCb (6.5-43.7 MBq/mmol) were from Amersham International (Buckinghamshire, United Kingdom). "C-labeled dextran (MI