Non-transferrin iron uptake by trophoblast cells in culture. Significance of a NADH-dependent ferrireductase.
This study shows that trophoblast cells in culture are able to take up 59Fe from both Fe(III)nitrilotriacetate (NTA) and Fe-ascorbate. Fe in the presence of ascorbate is assumed to be Fe(III) in equilibrium with Fe(II). Kinetic parameters for non-transferrin iron uptake are determined from initial rate experiments, yielding Vmax=366 pmol/mg protein/5 min and Km=0.96 microM for Fe(III)NTA and Vmax=4043 pmol/mg protein/5 min and Km= 1.3 microM for Fe-ascorbate. Since trophoblast cells in culture reduce extracellular Fe(III)CN, and uptake of 59Fe from Fe-ascorbate is higher than that from Fe(III)NTA, it is suggested that reduction of Fe(III) precedes uptake. Uptake of 59Fe from both Fe-ascorbate and Fe(III)NTA is inhibited by Fe(II)chelator ferrozine and membrane-impermeable Fe(III)CN, further supporting this hypothesis. Studies with microvillous membrane vesicles (MMV) and basal membrane vesicles (BMV) reveal the presence of a NADH-dependent ferrireductase. Reduction of Fe(III)CN follows Michaelis-Menten kinetics, both with respect to [NADH] and [Fe]. NADPH is ineffective as electron donor. The rate of Fe(III)CN reduction by BMV is 2.5 times higher compared to MMV, while Km values for Fe(III)CN and NADH are not significantly different. These results reveal that a transmembrane NADH-dependent ferrireductase plays a role in uptake of non-transferrin iron. The possibility that this enzyme system is involved in iron transfer across the basal membrane is discussed.
Department of Chemical Pathology, Erasmus University Rotterdam, The Netherlands.
C E
CE
Verrijt
M J
MJ
Kroos
M I
MI
Huijskes-Heins
H G
HG
van Eijk
J P
JP
van Dijk
D000328:Adult; D001205:Ascorbic Acid / Q000378:metabolism*; D002478:Cells, Cultured; D002824:Chorionic Villi / Q000378:metabolism; D038181:FMN Reductase; D005260:Female; D005290:Ferric Compounds / Q000378:metabolism*; D005292:Ferricyanides / Q000378:metabolism; D005296:Ferrous Compounds / Q000378:metabolism*; D005297:Ferrozine / Q000494:pharmacology; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology; D007502:Iron Chelating Agents / Q000494:pharmacology; D007504:Iron Radioisotopes / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D009571:Nitrilotriacetic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D011247:Pregnancy; D014168:Transferrin / Q000378:metabolism; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism*
D005290:Ferric Compounds; D005292:Ferricyanides; D005296:Ferrous Compounds; D007502:Iron Chelating Agents; D007504:Iron Radioisotopes; D014168:Transferrin; C051140:iron(II)-ascorbic acid complex; D005297:Ferrozine; D038181:FMN Reductase; D009247:NADH, NADPH Oxidoreductases; C023903:ferric citrate iron reductase; D009571:Nitrilotriacetic Acid; D001205:Ascorbic Acid; C020326:ferric nitrilotriacetate