The authors are retracting this Article. We were alerted to the possibility that the results described in the Article may be artefactual for the following reasons. Radiolabeled citrate binds to plastic culture dishes in the presence of ferric chloride. In the presence of excess unlabelled citrate and other iron chelators, this binding to plastic dishes may be inhibited, thus mimicking substrate selectivity and saturation kinetics. We have now performed additional control experiments using culture plates without cells present, and obtained the same results as those described in the Article. The binding of ferric citrate to the plastic dishes showed sodium-dependence because N-methyl-D-glucamine chloride that we routinely use to substitute for NaCl to study sodium-dependence of a transport system interfered with the process. As such, we are unable to support the conclusions regarding a new sodium-dependent ferric-citrate transporter in the mammalian cells. All authors agree to the retraction of the Article.
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